fix(installer): smooth in-place updates with auto-close of running app and overwrite

.gitea/workflows/build.yaml

@@ -0,0 +1,107 @@
+name: Build Windows Installer
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install NSIS and build tools
+        run: |
+          if command -v sudo >/dev/null 2>&1; then
+            sudo apt-get update
+            sudo apt-get install -y nsis wget curl tar unzip zip ca-certificates
+          else
+            apt-get update
+            apt-get install -y nsis wget curl tar unzip zip ca-certificates
+          fi
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.24'
+
+      - name: Build & test frontend
+        working-directory: frontend
+        run: |
+          npm install
+          npm test
+          npm run build
+
+      - name: Run Go unit tests
+        run: go test ./...
+
+      - name: Determine version
+        id: ver
+        run: |
+          if [[ "${GITHUB_REF}" == refs/tags/v* ]]; then
+            VER="${GITHUB_REF_NAME#v}"
+          else
+            VER="2.0.0-ci.${GITHUB_RUN_NUMBER}"
+          fi
+          echo "version=${VER}" >> "$GITHUB_OUTPUT"
+
+      - name: Embed Windows icon and manifest (.syso)
+        run: |
+          go run github.com/akavel/rsrc@v0.10.2 \
+            -arch amd64 \
+            -ico build/windows/icon.ico \
+            -manifest build/windows/app.manifest \
+            -o rsrc_windows_amd64.syso
+
+      - name: Cross-compile Windows binary (convert.exe)
+        env:
+          CGO_ENABLED: "0"
+          GOOS: windows
+          GOARCH: amd64
+        run: |
+          mkdir -p dist/bin
+          go build -tags desktop,production \
+            -ldflags="-H windowsgui -s -w -X main.Version=${{ steps.ver.outputs.version }}" \
+            -o dist/convert.exe .
+
+      - name: Download static FFmpeg & FFprobe for Windows
+        run: |
+          wget -q -O ffmpeg.zip "https://github.com/BtbN/FFmpeg-Builds/releases/download/latest/ffmpeg-master-latest-win64-gpl.zip"
+          unzip -j -q ffmpeg.zip "*/bin/ffmpeg.exe" "*/bin/ffprobe.exe" -d dist/bin/
+          rm -f ffmpeg.zip
+
+      - name: Package Portable ZIP
+        run: |
+          cd dist
+          zip -r "ConvertGUI-Portable-${{ steps.ver.outputs.version }}-win64.zip" convert.exe bin/
+
+      - name: Build Windows NSIS Installer
+        run: |
+          makensis -DVERSION="${{ steps.ver.outputs.version }}" installer/installer.nsi
+
+      - name: Upload Build Artifacts
+        uses: actions/upload-artifact@v3
+        with:
+          name: ConvertGUI-Windows-${{ steps.ver.outputs.version }}
+          path: |
+            dist/ConvertGUI-Setup-${{ steps.ver.outputs.version }}.exe
+            dist/ConvertGUI-Portable-${{ steps.ver.outputs.version }}-win64.zip
+
+      - name: Publish Gitea Release
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: akkuman/gitea-release-action@v1
+        with:
+          files: |
+            dist/ConvertGUI-Setup-${{ steps.ver.outputs.version }}.exe
+            dist/ConvertGUI-Portable-${{ steps.ver.outputs.version }}-win64.zip
+          name: Release ${{ github.ref_name }}

.gitignore

@@ -0,0 +1,14 @@
+# Binaries & build outputs
+/dist/
+/build/bin/
+/frontend/dist/
+/frontend/node_modules/
+*.exe
+*.syso
+*.log
+.DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+!.vscode/launch.json

.vscode/launch.json

@@ -1,19 +0,0 @@
-{
-    // Use IntelliSense to learn about possible attributes.
-    // Hover to view descriptions of existing attributes.
-    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
-    "version": "0.2.0",
-    "configurations": [
-        {
-            "name": "debug",
-            "type": "go",
-            "request": "launch",
-            "mode": "debug",
-            "program": "main.go",
-            "cwd": "${cwd}",
-            "console": "integratedTerminal",
-            // "args": ["--debug", "-i", "C:\\Users\\m4xx1m\\Videos\\NVIDIA\\Desktop\\Desktop 2025.07.09 - 13.10.33.02.mp4"]
-            "args": ["-i", "E:\\records\\Derail Valley\\Derail Valley 2025.08.14 - 02.18.46.02.mp4"]
-        },
-    ]
-}

README.md

@@ -0,0 +1,25 @@
+# ConvertGUI
+
+GUI video converter/trimmer powered by Go, Wails v2 (WebView2), and FFmpeg.
+
+## Features
+- Video preview with HTTP byte-range seeking + automatic MP4 proxy fallback (MKV/AVI/HEVC)
+- Interactive dual-handle timeline trim (`-ss`, `-to`), filmstrip thumbnails, loop-selection preview, `I`/`O` hotkeys
+- Optional spatial crop overlay (`crop=w:h:x:y`, even-dimension clamped)
+- Multi-audio stream handling (`amix=inputs=N:normalize=0`, single-track selection, or `-an` mute)
+- Speed multiplier (`0.25x`–`8x`) with `setpts` + chained `atempo`
+- Codecs: `libx264`, `h264_nvenc`, `libx265`, `hevc_nvenc`; HW decode (`none`, `nvdec`, `d3d11va`, `auto`); CRF/CQ, preset, tune, FPS
+- Windows Explorer context menu (`-i "%1"`), drag-and-drop, NSIS installer
+
+## Dev / Build
+```powershell
+cd frontend && npm install && npm run build
+cd .. && go test ./...
+$env:CGO_ENABLED="0"; $env:GOOS="windows"; $env:GOARCH="amd64"
+go build -tags desktop,production -ldflags="-H windowsgui -s -w" -o dist/convert.exe .
+```
+
+## CI
+- Workflow: `.gitea/workflows/build.yaml` (`ubuntu-latest`)
+- Builds `ConvertGUI-Setup-<version>.exe` (NSIS + bundled static `ffmpeg.exe`/`ffprobe.exe`) and `ConvertGUI-Portable-<version>-win64.zip`
+- Publishes release assets on `v*` tags via `akkuman/gitea-release-action@v1`

app.go

@@ -0,0 +1,315 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	goruntime "runtime"
+	"strings"
+	"sync"
+
+	"convert/internal/config"
+	"convert/internal/convert"
+	"convert/internal/media"
+	"convert/internal/preview"
+
+	"github.com/wailsapp/wails/v2/pkg/runtime"
+)
+
+type AppInfo struct {
+	Version     string           `json:"version"`
+	Binaries    media.Binaries   `json:"binaries"`
+	Config      config.AppConfig `json:"config"`
+	InitialFile string           `json:"initialFile"`
+}
+
+type LoadedVideo struct {
+	Info              *media.VideoInfo `json:"info"`
+	VideoID           string           `json:"videoId"`
+	PreviewURL        string           `json:"previewUrl"`
+	ProxyURL          string           `json:"proxyUrl"`
+	ProxyMergedURL    string           `json:"proxyMergedUrl"`
+	ThumbBaseURL      string           `json:"thumbBaseUrl"`
+	DefaultOutputPath string           `json:"defaultOutputPath"`
+}
+
+type App struct {
+	ctx         context.Context
+	initialFile string
+	cfg         config.AppConfig
+	bins        media.Binaries
+	previewSrv  *preview.Server
+	runner      *convert.Runner
+
+	mu          sync.RWMutex
+	currentInfo *media.VideoInfo
+}
+
+func NewApp(initialFile string) *App {
+	cfg := config.Load()
+	bins := media.FindBinaries(cfg.FFmpegPath, cfg.FFprobePath)
+	return &App{
+		initialFile: initialFile,
+		cfg:         cfg,
+		bins:        bins,
+		runner:      convert.NewRunner(),
+	}
+}
+
+func (a *App) startup(ctx context.Context) {
+	a.ctx = ctx
+
+	srv, err := preview.Start(a.bins.FFmpeg)
+	if err == nil {
+		a.previewSrv = srv
+	}
+}
+
+func (a *App) shutdown(_ context.Context) {
+	if a.runner != nil {
+		a.runner.Cancel()
+	}
+	if a.previewSrv != nil {
+		a.previewSrv.Close()
+	}
+}
+
+func (a *App) GetAppInfo() AppInfo {
+	a.mu.RLock()
+	defer a.mu.RUnlock()
+	return AppInfo{
+		Version:     Version,
+		Binaries:    a.bins,
+		Config:      a.cfg,
+		InitialFile: a.initialFile,
+	}
+}
+
+func (a *App) RefreshBinaries() media.Binaries {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	a.bins = media.FindBinaries(a.cfg.FFmpegPath, a.cfg.FFprobePath)
+	if a.previewSrv != nil {
+		a.previewSrv.SetFFmpeg(a.bins.FFmpeg)
+	}
+	return a.bins
+}
+
+func (a *App) SaveConfig(cfg config.AppConfig) (AppInfo, error) {
+	if err := config.Save(cfg); err != nil {
+		return AppInfo{}, err
+	}
+	a.mu.Lock()
+	a.cfg = cfg
+	a.bins = media.FindBinaries(cfg.FFmpegPath, cfg.FFprobePath)
+	if a.previewSrv != nil {
+		a.previewSrv.SetFFmpeg(a.bins.FFmpeg)
+	}
+	a.mu.Unlock()
+	return a.GetAppInfo(), nil
+}
+
+func (a *App) OpenVideoDialog() (string, error) {
+	return runtime.OpenFileDialog(a.ctx, runtime.OpenDialogOptions{
+		Title: "Select Video File",
+		Filters: []runtime.FileFilter{
+			{
+				DisplayName: "Video Files (*.mp4, *.mkv, *.mov, *.avi, *.webm, *.m4v, *.ts, *.flv)",
+				Pattern:     "*.mp4;*.mkv;*.mov;*.avi;*.webm;*.m4v;*.ts;*.flv;*.wmv",
+			},
+			{
+				DisplayName: "All Files (*.*)",
+				Pattern:     "*.*",
+			},
+		},
+	})
+}
+
+func (a *App) SaveVideoDialog(defaultPath string) (string, error) {
+	dir := filepath.Dir(defaultPath)
+	file := filepath.Base(defaultPath)
+	return runtime.SaveFileDialog(a.ctx, runtime.SaveDialogOptions{
+		Title:            "Save Output Video",
+		DefaultDirectory: dir,
+		DefaultFilename:  file,
+		Filters: []runtime.FileFilter{
+			{
+				DisplayName: "MP4 Video (*.mp4)",
+				Pattern:     "*.mp4",
+			},
+		},
+	})
+}
+
+func (a *App) SelectFFmpegDialog() (AppInfo, error) {
+	selected, err := runtime.OpenFileDialog(a.ctx, runtime.OpenDialogOptions{
+		Title: "Locate ffmpeg.exe",
+		Filters: []runtime.FileFilter{
+			{DisplayName: "ffmpeg executable", Pattern: "ffmpeg.exe;ffmpeg"},
+			{DisplayName: "All Files", Pattern: "*.*"},
+		},
+	})
+	if err != nil || selected == "" {
+		return a.GetAppInfo(), err
+	}
+
+	a.mu.Lock()
+	a.cfg.FFmpegPath = selected
+	dir := filepath.Dir(selected)
+	probeName := "ffprobe"
+	if goruntime.GOOS == "windows" {
+		probeName = "ffprobe.exe"
+	}
+	a.cfg.FFprobePath = filepath.Join(dir, probeName)
+	_ = config.Save(a.cfg)
+	a.bins = media.FindBinaries(a.cfg.FFmpegPath, a.cfg.FFprobePath)
+	if a.previewSrv != nil {
+		a.previewSrv.SetFFmpeg(a.bins.FFmpeg)
+	}
+	a.mu.Unlock()
+	return a.GetAppInfo(), nil
+}
+
+func (a *App) LoadVideo(path string) (*LoadedVideo, error) {
+	a.mu.RLock()
+	ffprobeBin := a.bins.FFprobe
+	suffix := a.cfg.OutputSuffix
+	a.mu.RUnlock()
+
+	info, err := media.Probe(ffprobeBin, path)
+	if err != nil {
+		return nil, err
+	}
+
+	a.mu.Lock()
+	a.currentInfo = info
+	a.mu.Unlock()
+
+	if a.previewSrv == nil {
+		return nil, fmt.Errorf("preview server is not running")
+	}
+
+	id := a.previewSrv.Register(info)
+	base := a.previewSrv.BaseURL()
+
+	return &LoadedVideo{
+		Info:              info,
+		VideoID:           id,
+		PreviewURL:        fmt.Sprintf("%s/video?id=%s", base, id),
+		ProxyURL:          fmt.Sprintf("%s/proxy?id=%s&merge=0", base, id),
+		ProxyMergedURL:    fmt.Sprintf("%s/proxy?id=%s&merge=1", base, id),
+		ThumbBaseURL:      fmt.Sprintf("%s/thumb?id=%s", base, id),
+		DefaultOutputPath: convert.DefaultOutputPath(path, suffix),
+	}, nil
+}
+
+func (a *App) PreviewCommand(req convert.Request) (string, error) {
+	a.mu.RLock()
+	info := a.currentInfo
+	a.mu.RUnlock()
+	if info == nil {
+		return "", nil
+	}
+	built, err := convert.BuildCommand(req, info)
+	if err != nil {
+		return "", err
+	}
+	parts := make([]string, 0, len(built.Args)+1)
+	parts = append(parts, "ffmpeg")
+	for _, arg := range built.Args {
+		if strings.ContainsAny(arg, " \t") {
+			parts = append(parts, `"`+arg+`"`)
+		} else {
+			parts = append(parts, arg)
+		}
+	}
+	return strings.Join(parts, " "), nil
+}
+
+func (a *App) StartConvert(req convert.Request) error {
+	a.mu.RLock()
+	info := a.currentInfo
+	ffmpegBin := a.bins.FFmpeg
+	a.mu.RUnlock()
+
+	if info == nil {
+		return fmt.Errorf("no video loaded")
+	}
+	if ffmpegBin == "" {
+		return fmt.Errorf("ffmpeg binary not found")
+	}
+	if a.runner.IsRunning() {
+		return fmt.Errorf("conversion already running")
+	}
+
+	built, err := convert.BuildCommand(req, info)
+	if err != nil {
+		return err
+	}
+
+	go func() {
+		err := a.runner.Run(a.ctx, ffmpegBin, built, func(p convert.Progress) {
+			runtime.EventsEmit(a.ctx, "convert:progress", p)
+		})
+		if err != nil {
+			runtime.EventsEmit(a.ctx, "convert:error", err.Error())
+			return
+		}
+		runtime.EventsEmit(a.ctx, "convert:done", built.OutputPath)
+	}()
+
+	return nil
+}
+
+func (a *App) CancelConvert() bool {
+	return a.runner.Cancel()
+}
+
+func (a *App) OpenInExplorer(path string) error {
+	if path == "" {
+		return nil
+	}
+	if goruntime.GOOS == "windows" {
+		cmd := exec.Command("explorer", "/select,", filepath.Clean(path))
+		return cmd.Start()
+	}
+	return exec.Command("xdg-open", filepath.Dir(path)).Start()
+}
+
+func (a *App) OpenOutputFile(path string) error {
+	if path == "" {
+		return nil
+	}
+	if goruntime.GOOS == "windows" {
+		cmd := exec.Command("cmd", "/c", "start", "", filepath.Clean(path))
+		media.HideCmdWindow(cmd)
+		return cmd.Start()
+	}
+	return exec.Command("xdg-open", path).Start()
+}
+
+func (a *App) WindowMinimise() {
+	if a.ctx != nil {
+		runtime.WindowMinimise(a.ctx)
+	}
+}
+
+func (a *App) WindowToggleMaximise() {
+	if a.ctx != nil {
+		runtime.WindowToggleMaximise(a.ctx)
+	}
+}
+
+func (a *App) WindowClose() {
+	if a.ctx != nil {
+		runtime.Quit(a.ctx)
+	}
+}
+
+func (a *App) WindowIsMaximised() bool {
+	if a.ctx != nil {
+		return runtime.WindowIsMaximised(a.ctx)
+	}
+	return false
+}

build/windows/app.manifest

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">
+  <assemblyIdentity version="2.0.0.0" processorArchitecture="amd64" name="ConvertGUI" type="win32"/>
+  <description>ConvertGUI Video Converter</description>
+  <dependency>
+    <dependentAssembly>
+      <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="6.0.0.0" processorArchitecture="*" publicKeyToken="6595b64144ccf1df" language="*"/>
+    </dependentAssembly>
+  </dependency>
+  <asmv3:application>
+    <asmv3:windowsSettings>
+      <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true/pm</dpiAware>
+      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
+    </asmv3:windowsSettings>
+  </asmv3:application>
+  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
+    <application>
+      <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}"/>
+      <supportedOS Id="{1f676c76-80e1-4239-95bb-83d0f6d0da78}"/>
+    </application>
+  </compatibility>
+</assembly>

ffprobe.go

@@ -1,36 +0,0 @@
-package main
-
-import (
-	"encoding/json"
-	"os/exec"
-)
-
-type ffprobeOutput struct {
-	Streams []struct {
-		CodecType string `json:"codec_type"`
-	} `json:"streams"`
-}
-
-func ffprobe(inputFile string) (*ffprobeOutput, error) {
-	var err error
-	var out ffprobeOutput
-
-	args := []string{
-		"-v", "quiet",
-		"-print_format", "json",
-		"-show_streams",
-		inputFile,
-	}
-	proc := exec.Command("ffprobe", args...)
-	stdout, err := proc.Output()
-	if err != nil {
-		return nil, err
-	}
-	// fmt.Println("read", string(stdout))
-
-	err = json.Unmarshal(stdout, &out)
-	if err != nil {
-		return nil, err
-	}
-	return &out, nil
-}

frontend/index.html

@@ -0,0 +1,12 @@
+<!doctype html>
+<html lang="ru">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>ConvertGUI</title>
+  </head>
+  <body>
+    <div id="app"></div>
+    <script type="module" src="/src/main.ts"></script>
+  </body>
+</html>

frontend/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "convert-gui-frontend",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc --noEmit && vite build",
+    "test": "node --experimental-strip-types --test src/timecode.test.ts src/wheel.test.ts"
+  },
+  "devDependencies": {
+    "typescript": "^5.7.2",
+    "vite": "^6.0.5"
+  }
+}

frontend/src/i18n.ts

@@ -0,0 +1,100 @@
+export type Lang = 'ru' | 'en';
+
+export const dict = {
+  ru: {
+    openVideo: 'Открыть видео',
+    dropTitle: 'Перетащите видео сюда',
+    dropHint: 'MP4, MKV, MOV, AVI, WebM — или нажмите «Открыть видео»',
+    ffmpegOk: 'FFmpeg готов',
+    ffmpegMissing: 'FFmpeg не найден (указать)',
+    setStart: 'Начало [I]',
+    setEnd: 'Конец [O]',
+    loopTrim: 'Повтор фрагмента',
+    previewMix: 'Микс дорожек в превью',
+    proxyLoading: 'Подготовка совместимого превью...',
+    trimStart: 'Начало (ss)',
+    trimEnd: 'Конец (to)',
+    clipDur: 'Длительность',
+    outDur: 'Итог (со скор.)',
+    resetTrim: 'Сбросить',
+    sectionVideo: 'Видео и качество',
+    encoder: 'Кодек',
+    hwDecode: 'Аппар. декодинг',
+    crf: 'Качество (CRF / CQ)',
+    preset: 'Пресет скорости',
+    tune: 'Тонкая настройка',
+    fps: 'FPS',
+    fpsOriginal: 'Оригинал',
+    sectionSpeed: 'Скорость воспроизведения',
+    sectionAudio: 'Аудиодорожки',
+    audioMerge: 'Объединить (amix)',
+    audioTrack: 'Одна дорожка',
+    audioMute: 'Без звука (-an)',
+    noAudio: 'В видео нет аудиодорожек',
+    sectionCrop: 'Кадрирование (Crop)',
+    cropEnable: 'Включить обрезку кадра',
+    sectionOutput: 'Выходной файл',
+    browse: 'Обзор...',
+    showCli: 'Команда FFmpeg',
+    copy: 'Копировать',
+    copied: 'Скопировано',
+    convertBtn: 'Конвертировать',
+    cancelBtn: 'Отмена',
+    doneTitle: 'Готово!',
+    openFolder: 'Открыть папку',
+    playOutput: 'Открыть файл',
+    crfHintBest: 'Почти без потерь',
+    crfHintBal: 'Оптимальный баланс',
+    crfHintComp: 'Сильное сжатие',
+    crfHintSmall: 'Минимальный размер',
+    eta: 'Осталось',
+  },
+  en: {
+    openVideo: 'Open Video',
+    dropTitle: 'Drop a video file here',
+    dropHint: 'MP4, MKV, MOV, AVI, WebM — or click "Open Video"',
+    ffmpegOk: 'FFmpeg ready',
+    ffmpegMissing: 'FFmpeg missing (locate)',
+    setStart: 'Set In [I]',
+    setEnd: 'Set Out [O]',
+    loopTrim: 'Loop Trim',
+    previewMix: 'Mix Audio in Preview',
+    proxyLoading: 'Preparing compatible preview...',
+    trimStart: 'Start (ss)',
+    trimEnd: 'End (to)',
+    clipDur: 'Selection',
+    outDur: 'Output (w/ speed)',
+    resetTrim: 'Reset',
+    sectionVideo: 'Video & Quality',
+    encoder: 'Encoder',
+    hwDecode: 'HW Decode',
+    crf: 'Quality (CRF / CQ)',
+    preset: 'Preset',
+    tune: 'Tune',
+    fps: 'FPS',
+    fpsOriginal: 'Original',
+    sectionSpeed: 'Playback Speed',
+    sectionAudio: 'Audio Streams',
+    audioMerge: 'Merge Tracks (amix)',
+    audioTrack: 'Single Track',
+    audioMute: 'Mute (-an)',
+    noAudio: 'No audio streams in source',
+    sectionCrop: 'Frame Crop',
+    cropEnable: 'Enable spatial crop',
+    sectionOutput: 'Output File',
+    browse: 'Browse...',
+    showCli: 'FFmpeg CLI',
+    copy: 'Copy',
+    copied: 'Copied',
+    convertBtn: 'Convert Video',
+    cancelBtn: 'Cancel',
+    doneTitle: 'Conversion Complete!',
+    openFolder: 'Show in Folder',
+    playOutput: 'Open File',
+    crfHintBest: 'Near lossless',
+    crfHintBal: 'Sweet spot',
+    crfHintComp: 'Compact size',
+    crfHintSmall: 'Heavy compression',
+    eta: 'ETA',
+  },
+} as const;

frontend/src/style.css

@@ -0,0 +1,833 @@
+:root {
+  /* Premiere / Pro-NLE Grayscale Palette */
+  --bg: #1c1c1c;
+  --panel: #252525;
+  --panel-2: #2b2b2b;
+  --panel-hover: #343434;
+  --panel-active: #3e3e3e;
+  --border: #383838;
+  --border-light: #484848;
+  --border-focus: #6e6e6e;
+
+  --text: #cccccc;
+  --text-bright: #f0f0f0;
+  --muted: #858585;
+  --dim: #5c5c5c;
+
+  /* Restrained Professional Accents */
+  --accent: #4a82c2;
+  --accent-hover: #5d93d4;
+  --accent-active: #3c6ea5;
+  --accent-glow: rgba(74, 130, 194, 0.22);
+
+  --trim-in: #4a82c2;
+  --trim-out: #8ba7c7;
+  --trim-band: rgba(74, 130, 194, 0.28);
+
+  --green: #4e8e5d;
+  --green-bg: rgba(78, 142, 93, 0.16);
+  --red: #a84646;
+  --red-bg: rgba(168, 70, 70, 0.16);
+  --amber: #a87d3e;
+  --amber-bg: rgba(168, 125, 62, 0.16);
+
+  --radius: 0px;
+  --mono: 'Cascadia Mono', 'Consolas', 'Segoe UI Mono', ui-monospace, Menlo, Monaco, monospace;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html,
+body {
+  margin: 0;
+  padding: 0;
+  height: 100%;
+  background: var(--bg);
+  color: var(--text);
+  font-family: 'Segoe UI', -apple-system, BlinkMacSystemFont, sans-serif;
+  font-size: 12px;
+  user-select: none;
+  overflow: hidden;
+  -webkit-font-smoothing: antialiased;
+}
+
+/* Professional Flat Dark Scrollbars */
+::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+::-webkit-scrollbar-track {
+  background: #181818;
+}
+::-webkit-scrollbar-thumb {
+  background: #3c3c3c;
+  border-radius: 0;
+  border: 1px solid #181818;
+}
+::-webkit-scrollbar-thumb:hover {
+  background: #505050;
+}
+* {
+  scrollbar-width: thin;
+  scrollbar-color: #3c3c3c #181818;
+}
+
+#app {
+  display: flex;
+  flex-direction: column;
+  height: 100vh;
+  box-sizing: border-box;
+  background: var(--bg);
+  border: 1px solid var(--border);
+  border-radius: 0;
+  overflow: hidden;
+  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.6);
+}
+
+body.maximized #app {
+  border: none;
+  box-shadow: none;
+}
+
+/* Top Bar / Titlebar */
+.topbar {
+  --wails-draggable: drag;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 10px;
+  padding: 0 0 0 12px;
+  height: 34px;
+  background: var(--panel);
+  border-bottom: 1px solid var(--border);
+  flex-shrink: 0;
+  user-select: none;
+}
+
+.topbar button,
+.topbar input,
+.topbar select,
+.topbar .file-pill,
+.win-controls {
+  --wails-draggable: no-drag;
+}
+
+/* Window Controls (Minimize, Maximize, Close) */
+.win-controls {
+  display: flex;
+  align-items: stretch;
+  height: 100%;
+  margin-left: 4px;
+  --wails-draggable: no-drag;
+}
+
+.win-btn {
+  width: 44px;
+  height: 100%;
+  border: none !important;
+  border-radius: 0 !important;
+  background: transparent !important;
+  color: var(--muted) !important;
+  display: flex !important;
+  align-items: center;
+  justify-content: center;
+  cursor: pointer;
+  padding: 0 !important;
+  transition: background 0.1s ease, color 0.1s ease;
+}
+
+.win-btn:hover {
+  background: #333333 !important;
+  color: var(--text-bright) !important;
+}
+
+.win-btn.close:hover {
+  background: #c42b1c !important;
+  color: #ffffff !important;
+}
+
+.brand {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.brand-icon {
+  width: 20px;
+  height: 20px;
+  border-radius: 0;
+  background: #333333;
+  border: 1px solid var(--border-light);
+  display: grid;
+  place-items: center;
+  font-weight: 700;
+  color: var(--accent);
+  font-size: 11px;
+}
+
+.brand-title {
+  font-weight: 700;
+  font-size: 12px;
+  letter-spacing: 0.5px;
+  color: var(--text-bright);
+  text-transform: uppercase;
+}
+
+.badge {
+  font-size: 10px;
+  padding: 1px 5px;
+  border-radius: 0;
+  background: #202020;
+  border: 1px solid var(--border);
+  color: var(--muted);
+  font-family: var(--mono);
+}
+
+.topbar-center {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  min-width: 0;
+  flex: 1;
+  justify-content: center;
+}
+
+.file-pill {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  background: #202020;
+  border: 1px solid var(--border);
+  padding: 3px 10px;
+  border-radius: 0;
+  max-width: 520px;
+  overflow: hidden;
+  white-space: nowrap;
+  text-overflow: ellipsis;
+  font-size: 11px;
+}
+
+.file-pill strong {
+  color: var(--text-bright);
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.file-meta {
+  color: var(--muted);
+  font-size: 11px;
+  font-family: var(--mono);
+}
+
+.topbar-right {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  height: 100%;
+}
+
+/* Professional Flat Buttons */
+button {
+  font-family: inherit;
+  font-size: 11px;
+  font-weight: 600;
+  border: 1px solid var(--border-light);
+  background: var(--panel-2);
+  color: var(--text);
+  padding: 5px 10px;
+  border-radius: 0;
+  cursor: pointer;
+  transition: all 0.1s ease;
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  line-height: 1.2;
+}
+
+button:hover:not(:disabled) {
+  border-color: var(--border-focus);
+  background: var(--panel-hover);
+  color: var(--text-bright);
+}
+
+button:active:not(:disabled) {
+  background: var(--panel-active);
+}
+
+button:disabled {
+  opacity: 0.35;
+  cursor: not-allowed;
+  border-color: var(--border);
+}
+
+button.primary {
+  background: var(--accent-active);
+  border-color: var(--accent);
+  color: #ffffff;
+}
+
+button.primary:hover:not(:disabled) {
+  background: var(--accent);
+  border-color: var(--accent-hover);
+  color: #ffffff;
+}
+
+button.danger {
+  background: var(--red-bg);
+  border-color: var(--red);
+  color: #e57373;
+}
+
+button.danger:hover:not(:disabled) {
+  background: rgba(168, 70, 70, 0.28);
+}
+
+button.pill-active {
+  background: #383838;
+  border-color: var(--accent);
+  color: var(--text-bright);
+}
+
+.status-pill {
+  font-size: 10px;
+  padding: 3px 8px;
+  border-radius: 0;
+  font-family: var(--mono);
+}
+
+.status-pill.ok {
+  background: var(--green-bg);
+  border-color: var(--green);
+  color: #98c998;
+}
+
+.status-pill.warn {
+  background: var(--amber-bg);
+  border-color: var(--amber);
+  color: #e0b06b;
+}
+
+/* Main Workspace Grid */
+.workspace {
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) 390px;
+  flex: 1;
+  min-height: 0;
+  background: var(--bg);
+}
+
+/* Left Stage */
+.stage-col {
+  display: flex;
+  flex-direction: column;
+  min-width: 0;
+  min-height: 0;
+  padding: 10px;
+  gap: 10px;
+}
+
+.player-wrap {
+  position: relative;
+  flex: 1;
+  min-height: 240px;
+  background: #141414;
+  border: 1px solid var(--border);
+  border-radius: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  overflow: hidden;
+}
+
+.video-stage {
+  position: relative;
+  display: block;
+  max-width: 100%;
+  max-height: 100%;
+  overflow: hidden;
+}
+
+video {
+  display: block;
+  width: 100%;
+  height: 100%;
+  object-fit: contain;
+  background: #000000;
+}
+
+.drop-overlay {
+  position: absolute;
+  inset: 10px;
+  border: 1px dashed var(--border-light);
+  border-radius: 0;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 8px;
+  text-align: center;
+  color: var(--muted);
+  background: rgba(20, 20, 20, 0.92);
+  cursor: pointer;
+}
+
+.drop-overlay.drag-over {
+  border-color: var(--accent);
+  background: rgba(74, 130, 194, 0.08);
+  color: var(--text-bright);
+}
+
+.drop-overlay h2 {
+  margin: 0;
+  font-size: 16px;
+  color: var(--text-bright);
+  font-weight: 600;
+}
+
+.proxy-banner {
+  position: absolute;
+  top: 8px;
+  left: 8px;
+  background: rgba(28, 28, 28, 0.92);
+  border: 1px solid var(--border-focus);
+  color: var(--text-bright);
+  padding: 4px 8px;
+  border-radius: 0;
+  font-size: 10px;
+  font-family: var(--mono);
+  z-index: 5;
+}
+
+/* Crop Overlay */
+.crop-overlay {
+  position: absolute;
+  inset: 0;
+  pointer-events: none;
+}
+
+.crop-box {
+  position: absolute;
+  border: 1px solid #ffffff;
+  box-shadow: 0 0 0 9999px rgba(0, 0, 0, 0.65);
+  cursor: move;
+  pointer-events: auto;
+}
+
+.crop-handle {
+  position: absolute;
+  width: 9px;
+  height: 9px;
+  background: #ffffff;
+  border: 1px solid #000000;
+  border-radius: 0;
+}
+.crop-handle.nw { top: -5px; left: -5px; cursor: nwse-resize; }
+.crop-handle.ne { top: -5px; right: -5px; cursor: nesw-resize; }
+.crop-handle.sw { bottom: -5px; left: -5px; cursor: nesw-resize; }
+.crop-handle.se { bottom: -5px; right: -5px; cursor: nwse-resize; }
+
+/* Transport Bar */
+.transport {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 6px;
+  flex-wrap: wrap;
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 0;
+  padding: 6px 10px;
+}
+
+.transport-group {
+  display: flex;
+  align-items: center;
+  gap: 5px;
+}
+
+.time-readout {
+  font-family: var(--mono);
+  font-size: 11px;
+  color: var(--text-bright);
+  background: #181818;
+  padding: 4px 8px;
+  border-radius: 0;
+  border: 1px solid var(--border);
+}
+
+/* Timeline & Trim */
+.timeline-card {
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 0;
+  padding: 8px 10px;
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+
+.timeline-track {
+  position: relative;
+  height: 52px;
+  background: #121212;
+  border: 1px solid var(--border);
+  border-radius: 0;
+  overflow: visible;
+  cursor: pointer;
+}
+
+.filmstrip {
+  position: absolute;
+  inset: 0;
+  display: grid;
+  grid-template-columns: repeat(12, 1fr);
+  overflow: hidden;
+  border-radius: 0;
+}
+
+.filmstrip img {
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+  opacity: 0.7;
+  pointer-events: none;
+}
+
+.trim-dim-left,
+.trim-dim-right {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  background: rgba(0, 0, 0, 0.75);
+  pointer-events: none;
+  border-radius: 0;
+}
+.trim-dim-left { left: 0; }
+.trim-dim-right { right: 0; }
+
+.trim-selection {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  background: var(--trim-band);
+  border-top: 2px solid var(--trim-in);
+  border-bottom: 2px solid var(--trim-in);
+  border-radius: 0;
+  pointer-events: none;
+}
+
+.trim-handle {
+  position: absolute;
+  top: -2px;
+  bottom: -2px;
+  width: 10px;
+  transform: translateX(-50%);
+  cursor: ew-resize;
+  z-index: 4;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.trim-handle::before {
+  content: '';
+  width: 5px;
+  height: 100%;
+  border-radius: 0;
+}
+
+.trim-handle.start::before {
+  background: var(--trim-in);
+  box-shadow: 0 0 4px rgba(0, 0, 0, 0.8);
+}
+
+.trim-handle.end::before {
+  background: var(--trim-out);
+  box-shadow: 0 0 4px rgba(0, 0, 0, 0.8);
+}
+
+.playhead {
+  position: absolute;
+  top: -4px;
+  bottom: -4px;
+  width: 1px;
+  background: #ffffff;
+  transform: translateX(-50%);
+  pointer-events: none;
+  z-index: 5;
+}
+
+.playhead::before {
+  content: '';
+  position: absolute;
+  top: -2px;
+  left: -4px;
+  border-left: 5px solid transparent;
+  border-right: 5px solid transparent;
+  border-top: 6px solid #4a82c2;
+}
+
+.trim-inputs {
+  display: grid;
+  grid-template-columns: 1fr 1fr auto auto auto;
+  gap: 6px;
+  align-items: end;
+}
+
+.field-mini {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+
+.field-mini label {
+  font-size: 10px;
+  color: var(--muted);
+  text-transform: uppercase;
+  letter-spacing: 0.4px;
+}
+
+.stat-chip {
+  background: #1a1a1a;
+  border: 1px solid var(--border);
+  border-radius: 0;
+  padding: 4px 8px;
+  font-family: var(--mono);
+  font-size: 11px;
+  white-space: nowrap;
+  color: var(--text);
+}
+
+/* Right Settings Panel */
+.settings-col {
+  background: var(--panel);
+  border-left: 1px solid var(--border);
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
+}
+
+.settings-scroll {
+  flex: 1;
+  overflow-y: auto;
+  padding: 10px;
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+.card {
+  background: var(--panel-2);
+  border: 1px solid var(--border);
+  border-radius: 0;
+  padding: 10px;
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+
+.card-title {
+  font-size: 11px;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: 0.6px;
+  color: var(--muted);
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  border-bottom: 1px solid #353535;
+  padding-bottom: 4px;
+}
+
+.grid-2 {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 6px;
+}
+
+.grid-4 {
+  display: grid;
+  grid-template-columns: repeat(4, 1fr);
+  gap: 5px;
+}
+
+.field {
+  display: flex;
+  flex-direction: column;
+  gap: 3px;
+}
+
+.field label {
+  font-size: 10px;
+  color: var(--muted);
+  display: flex;
+  justify-content: space-between;
+  letter-spacing: 0.3px;
+}
+
+input[type='text'],
+input[type='number'],
+select {
+  width: 100%;
+  background: #1c1c1c;
+  border: 1px solid var(--border-light);
+  color: var(--text-bright);
+  padding: 5px 7px;
+  border-radius: 0;
+  font-family: inherit;
+  font-size: 11px;
+  outline: none;
+  transition: border-color 0.1s ease;
+}
+
+input[type='text']:focus,
+input[type='number']:focus,
+select:focus {
+  border-color: var(--border-focus);
+}
+
+input.mono {
+  font-family: var(--mono);
+}
+
+/* Premiere-Style Rectangular Slider */
+input[type='range'] {
+  width: 100%;
+  accent-color: var(--accent);
+  background: transparent;
+  cursor: pointer;
+  height: 16px;
+}
+
+.pill-row {
+  display: flex;
+  gap: 4px;
+  flex-wrap: wrap;
+}
+
+.pill-btn {
+  padding: 4px 8px;
+  font-size: 10px;
+  border-radius: 0;
+  background: #242424;
+  border: 1px solid var(--border-light);
+  color: var(--text);
+}
+
+.pill-btn:hover {
+  background: #333333;
+  color: var(--text-bright);
+}
+
+.pill-btn.pill-active {
+  background: #3c3c3c;
+  border-color: var(--border-focus);
+  color: #ffffff;
+}
+
+.track-list {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.track-item {
+  display: flex;
+  align-items: center;
+  gap: 7px;
+  font-size: 11px;
+  background: #202020;
+  border: 1px solid var(--border);
+  padding: 4px 7px;
+  border-radius: 0;
+}
+
+.input-row {
+  display: flex;
+  gap: 5px;
+}
+
+.input-row input {
+  flex: 1;
+}
+
+.cli-box {
+  background: #141414;
+  border: 1px solid var(--border);
+  border-radius: 0;
+  padding: 6px 8px;
+  font-family: var(--mono);
+  font-size: 10px;
+  color: #9e9e9e;
+  word-break: break-all;
+  max-height: 80px;
+  overflow-y: auto;
+  user-select: text;
+}
+
+/* Sticky Bottom Action */
+.action-footer {
+  padding: 10px;
+  border-top: 1px solid var(--border);
+  background: var(--panel);
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.progress-wrap {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.progress-bar-bg {
+  height: 6px;
+  background: #141414;
+  border-radius: 0;
+  overflow: hidden;
+  border: 1px solid var(--border);
+}
+
+.progress-bar-fill {
+  height: 100%;
+  width: 0%;
+  background: var(--accent);
+  border-radius: 0;
+  transition: width 0.15s linear;
+}
+
+.progress-meta {
+  display: flex;
+  justify-content: space-between;
+  font-family: var(--mono);
+  font-size: 10px;
+  color: var(--muted);
+}
+
+.done-banner {
+  background: #1c261e;
+  border: 1px solid var(--green);
+  border-radius: 0;
+  padding: 8px;
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.error-banner {
+  background: #2b1d1d;
+  border: 1px solid var(--red);
+  border-radius: 0;
+  padding: 7px 8px;
+  color: #e57373;
+  font-size: 11px;
+  word-break: break-word;
+  user-select: text;
+}
+
+.hidden {
+  display: none !important;
+}

frontend/src/timecode.test.ts

@@ -0,0 +1,31 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import { formatTimecode, parseTimecode, formatBytes, clampTrimRange } from './timecode.ts';
+
+describe('timecode helpers', () => {
+  it('formats seconds to HH:MM:SS.mmm', () => {
+    assert.equal(formatTimecode(0), '00:00:00.000');
+    assert.equal(formatTimecode(65.25), '00:01:05.250');
+    assert.equal(formatTimecode(3661.5), '01:01:01.500');
+    assert.equal(formatTimecode(125, false), '02:05');
+  });
+
+  it('parses numeric seconds and HH:MM:SS.mmm', () => {
+    assert.equal(parseTimecode('42.5'), 42.5);
+    assert.equal(parseTimecode('01:05.250'), 65.25);
+    assert.equal(parseTimecode('01:02:03.5'), 3723.5);
+    assert.equal(parseTimecode('invalid'), null);
+    assert.equal(parseTimecode('00:75:00'), null);
+  });
+
+  it('clamps trim range cleanly', () => {
+    assert.deepEqual(clampTrimRange(-5, 200, 60), { start: 0, end: 60 });
+    assert.deepEqual(clampTrimRange(30, 30, 60, 0.5), { start: 30, end: 30.5 });
+    assert.deepEqual(clampTrimRange(59.9, 60, 60, 0.5), { start: 59.5, end: 60 });
+  });
+
+  it('formats bytes', () => {
+    assert.equal(formatBytes(0), '0 B');
+    assert.equal(formatBytes(1024 * 1024 * 25.4), '25.4 MB');
+  });
+});

frontend/src/timecode.ts

@@ -0,0 +1,94 @@
+export function formatTimecode(seconds: number, includeMillis = true): string {
+  if (!Number.isFinite(seconds) || seconds < 0) seconds = 0;
+  const totalMs = Math.round(seconds * 1000);
+  const ms = totalMs % 1000;
+  const totalSec = Math.floor(totalMs / 1000);
+  const s = totalSec % 60;
+  const totalMin = Math.floor(totalSec / 60);
+  const m = totalMin % 60;
+  const h = Math.floor(totalMin / 60);
+
+  const hh = String(h).padStart(2, '0');
+  const mm = String(m).padStart(2, '0');
+  const ss = String(s).padStart(2, '0');
+  if (!includeMillis) {
+    return h > 0 ? `${hh}:${mm}:${ss}` : `${mm}:${ss}`;
+  }
+  const mmm = String(ms).padStart(3, '0');
+  return `${hh}:${mm}:${ss}.${mmm}`;
+}
+
+export function parseTimecode(input: string): number | null {
+  const s = input.trim();
+  if (!s) return null;
+
+  if (/^\d+(\.\d+)?$/.test(s)) {
+    const val = Number(s);
+    return Number.isFinite(val) && val >= 0 ? val : null;
+  }
+
+  const parts = s.split(':');
+  if (parts.length < 2 || parts.length > 3) return null;
+
+  let h = 0;
+  let m = 0;
+  let sec = 0;
+  if (parts.length === 2) {
+    m = Number(parts[0]);
+    sec = Number(parts[1]);
+  } else {
+    h = Number(parts[0]);
+    m = Number(parts[1]);
+    sec = Number(parts[2]);
+  }
+
+  if (
+    !Number.isFinite(h) ||
+    !Number.isFinite(m) ||
+    !Number.isFinite(sec) ||
+    h < 0 ||
+    m < 0 ||
+    m >= 60 ||
+    sec < 0 ||
+    sec >= 60
+  ) {
+    return null;
+  }
+
+  return h * 3600 + m * 60 + sec;
+}
+
+export function formatBytes(bytes: number): string {
+  if (!Number.isFinite(bytes) || bytes <= 0) return '0 B';
+  const units = ['B', 'KB', 'MB', 'GB', 'TB'];
+  let idx = 0;
+  let val = bytes;
+  while (val >= 1024 && idx < units.length - 1) {
+    val /= 1024;
+    idx++;
+  }
+  return `${val >= 100 || idx === 0 ? val.toFixed(0) : val.toFixed(1)} ${units[idx]}`;
+}
+
+export function clampTrimRange(
+  start: number,
+  end: number,
+  duration: number,
+  minGap = 0.05
+): { start: number; end: number } {
+  const dur = Math.max(0, duration);
+  let s = Math.max(0, Math.min(start, dur));
+  let e = Math.max(0, Math.min(end, dur));
+  if (dur <= minGap) {
+    return { start: 0, end: dur };
+  }
+  if (e - s < minGap) {
+    if (s + minGap <= dur) {
+      e = s + minGap;
+    } else {
+      s = Math.max(0, dur - minGap);
+      e = dur;
+    }
+  }
+  return { start: s, end: e };
+}

frontend/src/wails.d.ts

@@ -0,0 +1,142 @@
+export interface AudioStream {
+  index: number;
+  audioOrder: number;
+  codec: string;
+  channels: number;
+  channelLayout: string;
+  sampleRate: string;
+  language: string;
+  title: string;
+}
+
+export interface VideoInfo {
+  path: string;
+  fileName: string;
+  extension: string;
+  container: string;
+  sizeBytes: number;
+  duration: number;
+  bitRate: number;
+  width: number;
+  height: number;
+  fps: number;
+  videoCodec: string;
+  pixFmt: string;
+  audioStreams: AudioStream[];
+  browserNative: boolean;
+}
+
+export interface Binaries {
+  ffmpeg: string;
+  ffprobe: string;
+  source: string;
+}
+
+export interface AppConfig {
+  language: 'ru' | 'en' | string;
+  ffmpegPath: string;
+  ffprobePath: string;
+  defaultEncoder: string;
+  defaultHwDecode: string;
+  defaultPreset: string;
+  defaultCrf: number;
+  defaultFps: number;
+  defaultTune: string;
+  defaultMergeAudio: boolean;
+  outputSuffix: string;
+}
+
+export interface AppInfo {
+  version: string;
+  binaries: Binaries;
+  config: AppConfig;
+  initialFile: string;
+}
+
+export interface LoadedVideo {
+  info: VideoInfo;
+  videoId: string;
+  previewUrl: string;
+  proxyUrl: string;
+  proxyMergedUrl: string;
+  thumbBaseUrl: string;
+  defaultOutputPath: string;
+}
+
+export interface CropRect {
+  enabled: boolean;
+  x: number;
+  y: number;
+  w: number;
+  h: number;
+}
+
+export interface ConvertRequest {
+  inputPath: string;
+  outputPath: string;
+  trimStart: number;
+  trimEnd: number;
+  encoder: string;
+  hwDecode: string;
+  preset: string;
+  crf: number;
+  tune: string;
+  fps: number;
+  speed: number;
+  audioMode: 'merge' | 'track' | 'mute';
+  audioTrack: number;
+  selectedTracks: number[];
+  crop: CropRect;
+  fastStart: boolean;
+  overwrite: boolean;
+}
+
+export interface ProgressEvent {
+  percent: number;
+  outTimeSec: number;
+  totalSec: number;
+  fps: number;
+  speed: string;
+  totalSize: number;
+  etaSec: number;
+  done: boolean;
+  error?: string;
+  outputPath?: string;
+  outputBytes?: number;
+}
+
+declare global {
+  interface Window {
+    go?: {
+      main?: {
+        App?: {
+          GetAppInfo(): Promise<AppInfo>;
+          RefreshBinaries(): Promise<Binaries>;
+          SaveConfig(cfg: AppConfig): Promise<AppInfo>;
+          OpenVideoDialog(): Promise<string>;
+          SaveVideoDialog(defaultPath: string): Promise<string>;
+          SelectFFmpegDialog(): Promise<AppInfo>;
+          LoadVideo(path: string): Promise<LoadedVideo>;
+          PreviewCommand(req: ConvertRequest): Promise<string>;
+          StartConvert(req: ConvertRequest): Promise<void>;
+          CancelConvert(): Promise<boolean>;
+          OpenInExplorer(path: string): Promise<void>;
+          OpenOutputFile(path: string): Promise<void>;
+          WindowMinimise(): Promise<void>;
+          WindowToggleMaximise(): Promise<void>;
+          WindowClose(): Promise<void>;
+          WindowIsMaximised(): Promise<boolean>;
+        };
+      };
+    };
+    runtime?: {
+      EventsOn(eventName: string, callback: (...args: any[]) => void): () => void;
+      OnFileDrop?(callback: (x: number, y: number, paths: string[]) => void, useDropTarget?: boolean): void;
+      OnFileDropOff?(): void;
+      WindowMinimise?(): void;
+      WindowToggleMaximise?(): void;
+      WindowClose?(): void;
+      WindowIsMaximised?(): Promise<boolean>;
+    };
+  }
+}

frontend/src/wheel.test.ts

@@ -0,0 +1,39 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import { WheelStepper, nextEnabledOptionIndex, stepNumericValue } from './wheel.ts';
+
+describe('wheel helpers', () => {
+  it('triggers immediately on mouse wheel notch and accumulates touchpad micro-deltas', () => {
+    const stepper = new WheelStepper(40, 250);
+    assert.equal(stepper.feed({ deltaY: 100, nowMs: 1000 }), 1);
+    assert.equal(stepper.feed({ deltaY: -100, nowMs: 1050 }), -1);
+
+    // Touchpad micro-events accumulate until threshold
+    assert.equal(stepper.feed({ deltaY: 15, nowMs: 1100 }), 0);
+    assert.equal(stepper.feed({ deltaY: 15, nowMs: 1120 }), 0);
+    assert.equal(stepper.feed({ deltaY: 15, nowMs: 1140 }), 1);
+
+    // Reversing direction clears prior partial delta
+    assert.equal(stepper.feed({ deltaY: 20, nowMs: 1200 }), 0);
+    assert.equal(stepper.feed({ deltaY: -25, nowMs: 1220 }), 0);
+    assert.equal(stepper.feed({ deltaY: -20, nowMs: 1240 }), -1);
+
+    // Idle reset discards stale delta
+    assert.equal(stepper.feed({ deltaY: 30, nowMs: 1300 }), 0);
+    assert.equal(stepper.feed({ deltaY: 20, nowMs: 1700 }), 0);
+  });
+
+  it('skips disabled options and clamps at bounds', () => {
+    const flags = [false, true, false, false];
+    assert.equal(nextEnabledOptionIndex(0, flags, 1), 2);
+    assert.equal(nextEnabledOptionIndex(2, flags, -1), 0);
+    assert.equal(nextEnabledOptionIndex(0, flags, -1), 0);
+    assert.equal(nextEnabledOptionIndex(3, flags, 1), 3);
+  });
+
+  it('steps numeric values cleanly without float drift', () => {
+    assert.equal(stepNumericValue(1.1, 0.05, 0.25, 8, 1), 1.15);
+    assert.equal(stepNumericValue(0.25, 0.05, 0.25, 8, -1), 0.25);
+    assert.equal(stepNumericValue(51, 1, 0, 51, 1), 51);
+  });
+});

frontend/src/wheel.ts

@@ -0,0 +1,165 @@
+/**
+ * Pure wheel-delta accumulator and control-stepping helpers for mouse-wheel
+ * switching on select, range, and number inputs.
+ */
+
+export interface WheelSample {
+  deltaY: number;
+  deltaX?: number;
+  deltaMode?: number;
+  nowMs?: number;
+}
+
+export class WheelStepper {
+  private accum = 0;
+  private lastMs = 0;
+  private readonly threshold: number;
+  private readonly resetMs: number;
+
+  constructor(threshold = 40, resetMs = 250) {
+    this.threshold = threshold;
+    this.resetMs = resetMs;
+  }
+
+  /**
+   * Feeds a wheel event and returns +1 (down/next), -1 (up/prev), or 0 (not enough delta yet).
+   */
+  feed(sample: WheelSample): 1 | -1 | 0 {
+    const now = sample.nowMs ?? Date.now();
+    if (this.lastMs > 0 && now - this.lastMs > this.resetMs) {
+      this.accum = 0;
+    }
+    this.lastMs = now;
+
+    const dx = sample.deltaX ?? 0;
+    let delta = Math.abs(sample.deltaY) >= Math.abs(dx) ? sample.deltaY : dx;
+    if (delta === 0) return 0;
+
+    if (sample.deltaMode === 1) delta *= 33;
+    else if (sample.deltaMode === 2) delta *= 100;
+
+    if (this.accum !== 0 && Math.sign(delta) !== Math.sign(this.accum)) {
+      this.accum = 0;
+    }
+
+    this.accum += delta;
+    if (Math.abs(this.accum) < this.threshold) {
+      return 0;
+    }
+
+    const dir: 1 | -1 = this.accum > 0 ? 1 : -1;
+    this.accum = 0;
+    return dir;
+  }
+}
+
+export function nextEnabledOptionIndex(
+  currentIndex: number,
+  disabledFlags: readonly boolean[],
+  dir: 1 | -1
+): number {
+  let idx = currentIndex + dir;
+  while (idx >= 0 && idx < disabledFlags.length && disabledFlags[idx]) {
+    idx += dir;
+  }
+  if (idx < 0 || idx >= disabledFlags.length) {
+    return currentIndex;
+  }
+  return idx;
+}
+
+export function stepNumericValue(
+  current: number,
+  step: number,
+  min: number,
+  max: number,
+  dir: 1 | -1
+): number {
+  const safeStep = Number.isFinite(step) && step > 0 ? step : 1;
+  const raw = current + dir * safeStep;
+  const clamped = Math.max(min, Math.min(max, raw));
+  // Round to avoid binary floating-point drift on fractional steps (e.g. 0.05)
+  return Number(clamped.toFixed(6));
+}
+
+function attachWheelStep(
+  el: HTMLElement,
+  isDisabled: () => boolean,
+  onStep: (dir: 1 | -1) => void
+) {
+  const stepper = new WheelStepper();
+  el.addEventListener(
+    'wheel',
+    (e: WheelEvent) => {
+      if (isDisabled()) return;
+      e.preventDefault();
+      e.stopPropagation();
+
+      const dir = stepper.feed({
+        deltaY: e.deltaY,
+        deltaX: e.deltaX,
+        deltaMode: e.deltaMode,
+      });
+      if (dir !== 0) {
+        onStep(dir);
+      }
+    },
+    { passive: false }
+  );
+}
+
+export function bindWheelControls(root: ParentNode = document) {
+  root.querySelectorAll<HTMLSelectElement>('select').forEach((sel) => {
+    attachWheelStep(
+      sel,
+      () => sel.disabled || sel.options.length <= 1,
+      (dir) => {
+        const disabled = Array.from(sel.options, (opt) => opt.disabled);
+        const nextIdx = nextEnabledOptionIndex(sel.selectedIndex, disabled, dir);
+        if (nextIdx !== sel.selectedIndex) {
+          sel.selectedIndex = nextIdx;
+          sel.dispatchEvent(new Event('change', { bubbles: true }));
+        }
+      }
+    );
+  });
+
+  root.querySelectorAll<HTMLInputElement>('input[type="range"]').forEach((rng) => {
+    attachWheelStep(
+      rng,
+      () => rng.disabled,
+      (dir) => {
+        const step = Number(rng.step) || 1;
+        const min = rng.min !== '' ? Number(rng.min) : 0;
+        const max = rng.max !== '' ? Number(rng.max) : 100;
+        const cur = Number(rng.value);
+        // Wheel up (dir === -1) increases slider value; wheel down (dir === 1) decreases it.
+        const next = stepNumericValue(cur, step, min, max, dir === -1 ? 1 : -1);
+        if (next !== cur) {
+          rng.value = String(next);
+          rng.dispatchEvent(new Event('input', { bubbles: true }));
+          rng.dispatchEvent(new Event('change', { bubbles: true }));
+        }
+      }
+    );
+  });
+
+  root.querySelectorAll<HTMLInputElement>('input[type="number"]').forEach((inp) => {
+    attachWheelStep(
+      inp,
+      () => inp.disabled || inp.readOnly,
+      (dir) => {
+        const step = Number(inp.step) || 1;
+        const min = inp.min !== '' ? Number(inp.min) : -Infinity;
+        const max = inp.max !== '' ? Number(inp.max) : Infinity;
+        const cur = Number(inp.value) || 0;
+        const next = stepNumericValue(cur, step, min, max, dir === -1 ? 1 : -1);
+        if (next !== cur) {
+          inp.value = String(next);
+          inp.dispatchEvent(new Event('input', { bubbles: true }));
+          inp.dispatchEvent(new Event('change', { bubbles: true }));
+        }
+      }
+    );
+  });
+}

frontend/tsconfig.json

@@ -0,0 +1,19 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "useDefineForClassFields": true,
+    "module": "ESNext",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "skipLibCheck": true,
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "isolatedModules": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true
+  },
+  "include": ["src"],
+  "exclude": ["src/**/*.test.ts"]
+}

frontend/vite.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+  base: './',
+  build: {
+    outDir: 'dist',
+    emptyOutDir: true,
+    target: 'es2022',
+  },
+});

go.mod

@@ -1,3 +1,35 @@
 module convert
 
-go 1.17
+go 1.24
+
+require github.com/wailsapp/wails/v2 v2.10.2
+
+require (
+	github.com/bep/debounce v1.2.1 // indirect
+	github.com/go-ole/go-ole v1.3.0 // indirect
+	github.com/godbus/dbus/v5 v5.1.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/gorilla/websocket v1.5.3 // indirect
+	github.com/jchv/go-winloader v0.0.0-20210711035445-715c2860da7e // indirect
+	github.com/labstack/echo/v4 v4.13.3 // indirect
+	github.com/labstack/gommon v0.4.2 // indirect
+	github.com/leaanthony/go-ansi-parser v1.6.1 // indirect
+	github.com/leaanthony/gosod v1.0.4 // indirect
+	github.com/leaanthony/slicer v1.6.0 // indirect
+	github.com/leaanthony/u v1.1.1 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/rivo/uniseg v0.4.7 // indirect
+	github.com/samber/lo v1.49.1 // indirect
+	github.com/tkrajina/go-reflector v0.5.8 // indirect
+	github.com/valyala/bytebufferpool v1.0.0 // indirect
+	github.com/valyala/fasttemplate v1.2.2 // indirect
+	github.com/wailsapp/go-webview2 v1.0.19 // indirect
+	github.com/wailsapp/mimetype v1.4.1 // indirect
+	golang.org/x/crypto v0.33.0 // indirect
+	golang.org/x/net v0.35.0 // indirect
+	golang.org/x/sys v0.30.0 // indirect
+	golang.org/x/text v0.22.0 // indirect
+)

go.sum

@@ -0,0 +1,81 @@
+github.com/bep/debounce v1.2.1 h1:v67fRdBA9UQu2NhLFXrSg0Brw7CexQekrBwDMM8bzeY=
+github.com/bep/debounce v1.2.1/go.mod h1:H8yggRPQKLUhUoqrJC1bO2xNya7vanpDl7xR3ISbCJ0=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-ole/go-ole v1.3.0 h1:Dt6ye7+vXGIKZ7Xtk4s6/xVdGDQynvom7xCFEdWr6uE=
+github.com/go-ole/go-ole v1.3.0/go.mod h1:5LS6F96DhAwUc7C+1HLexzMXY1xGRSryjyPPKW6zv78=
+github.com/godbus/dbus/v5 v5.1.0 h1:4KLkAxT3aOY8Li4FRJe/KvhoNFFxo0m6fNuFUO8QJUk=
+github.com/godbus/dbus/v5 v5.1.0/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/jchv/go-winloader v0.0.0-20210711035445-715c2860da7e h1:Q3+PugElBCf4PFpxhErSzU3/PY5sFL5Z6rfv4AbGAck=
+github.com/jchv/go-winloader v0.0.0-20210711035445-715c2860da7e/go.mod h1:alcuEEnZsY1WQsagKhZDsoPCRoOijYqhZvPwLG0kzVs=
+github.com/labstack/echo/v4 v4.13.3 h1:pwhpCPrTl5qry5HRdM5FwdXnhXSLSY+WE+YQSeCaafY=
+github.com/labstack/echo/v4 v4.13.3/go.mod h1:o90YNEeQWjDozo584l7AwhJMHN0bOC4tAfg+Xox9q5g=
+github.com/labstack/gommon v0.4.2 h1:F8qTUNXgG1+6WQmqoUWnz8WiEU60mXVVw0P4ht1WRA0=
+github.com/labstack/gommon v0.4.2/go.mod h1:QlUFxVM+SNXhDL/Z7YhocGIBYOiwB0mXm1+1bAPHPyU=
+github.com/leaanthony/debme v1.2.1 h1:9Tgwf+kjcrbMQ4WnPcEIUcQuIZYqdWftzZkBr+i/oOc=
+github.com/leaanthony/debme v1.2.1/go.mod h1:3V+sCm5tYAgQymvSOfYQ5Xx2JCr+OXiD9Jkw3otUjiA=
+github.com/leaanthony/go-ansi-parser v1.6.1 h1:xd8bzARK3dErqkPFtoF9F3/HgN8UQk0ed1YDKpEz01A=
+github.com/leaanthony/go-ansi-parser v1.6.1/go.mod h1:+vva/2y4alzVmmIEpk9QDhA7vLC5zKDTRwfZGOp3IWU=
+github.com/leaanthony/gosod v1.0.4 h1:YLAbVyd591MRffDgxUOU1NwLhT9T1/YiwjKZpkNFeaI=
+github.com/leaanthony/gosod v1.0.4/go.mod h1:GKuIL0zzPj3O1SdWQOdgURSuhkF+Urizzxh26t9f1cw=
+github.com/leaanthony/slicer v1.6.0 h1:1RFP5uiPJvT93TAHi+ipd3NACobkW53yUiBqZheE/Js=
+github.com/leaanthony/slicer v1.6.0/go.mod h1:o/Iz29g7LN0GqH3aMjWAe90381nyZlDNquK+mtH2Fj8=
+github.com/leaanthony/u v1.1.1 h1:TUFjwDGlNX+WuwVEzDqQwC2lOv0P4uhTQw7CMFdiK7M=
+github.com/leaanthony/u v1.1.1/go.mod h1:9+o6hejoRljvZ3BzdYlVL0JYCwtnAsVuN9pVTQcaRfI=
+github.com/matryer/is v1.4.0/go.mod h1:8I/i5uYgLzgsgEloJE1U6xx5HkBQpAZvepWuujKwMRU=
+github.com/matryer/is v1.4.1 h1:55ehd8zaGABKLXQUe2awZ99BD/PTc2ls+KV/dXphgEQ=
+github.com/matryer/is v1.4.1/go.mod h1:8I/i5uYgLzgsgEloJE1U6xx5HkBQpAZvepWuujKwMRU=
+github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
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install.ps1

@@ -1,39 +0,0 @@
-[Console]::OutputEncoding = [System.Text.Encoding]::UTF8
-$OutputEncoding = [System.Text.Encoding]::UTF8
-
-function pressEnterToExit {
-    Write-Host "Press Enter to exit... " -NoNewline
-    [void][System.Console]::ReadLine()
-}
-
-$installPath = Join-Path $HOME "programs\convert"
-New-Item -Force -ItemType Directory $installPath | Out-Null
-
-$executablePath = Join-Path $installPath convert.exe
-go build -o $executablePath
-
-if ($LASTEXITCODE -eq 0) {
-    Write-Host "✅ built: $executablePath"
-} else {
-    Write-Host "❌ build error"
-    pressEnterToExit
-    exit $LASTEXITCODE
-}
-
-reg add "HKCU\Software\Classes\SystemFileAssociations\.mp4\shell\convert" /ve /d "convert" /f > $null
-if ($LASTEXITCODE -ne 0) {
-    Write-Host "❌ reg error"
-    pressEnterToExit
-    exit $LASTEXITCODE
-} 
-
-$command = $executablePath + " -i `"%1`""
-reg add "HKCU\Software\Classes\SystemFileAssociations\.mp4\shell\convert\command" /ve /d $command /f  > $null
-if ($LASTEXITCODE -ne 0) {
-    Write-Host "❌ reg error"
-    pressEnterToExit
-    exit $LASTEXITCODE
-}
-
-Write-Host "✅ reg values added"
-pressEnterToExit

installer/installer.nsi

@@ -0,0 +1,156 @@
+Unicode True
+!include "MUI2.nsh"
+
+!ifndef VERSION
+  !define VERSION "2.0.0"
+!endif
+
+!define APP_NAME "ConvertGUI"
+!define EXE_NAME "convert.exe"
+!define UNINSTALL_REG "Software\Microsoft\Windows\CurrentVersion\Uninstall\${APP_NAME}"
+
+Name "${APP_NAME} ${VERSION}"
+OutFile "../dist/ConvertGUI-Setup-${VERSION}.exe"
+InstallDir "$LOCALAPPDATA\Programs\${APP_NAME}"
+InstallDirRegKey HKCU "Software\${APP_NAME}" "InstallDir"
+RequestExecutionLevel user
+SetCompressor /SOLID lzma
+SetOverwrite on
+
+!define MUI_ABORTWARNING
+!define MUI_ICON "../build/windows/icon.ico"
+!define MUI_UNICON "../build/windows/icon.ico"
+
+!insertmacro MUI_PAGE_WELCOME
+!insertmacro MUI_PAGE_COMPONENTS
+!insertmacro MUI_PAGE_DIRECTORY
+!insertmacro MUI_PAGE_INSTFILES
+!define MUI_FINISHPAGE_RUN "$INSTDIR\${EXE_NAME}"
+!insertmacro MUI_PAGE_FINISH
+
+!insertmacro MUI_UNPAGE_CONFIRM
+!insertmacro MUI_UNPAGE_INSTFILES
+
+!insertmacro MUI_LANGUAGE "English"
+!insertmacro MUI_LANGUAGE "Russian"
+
+!macro RegisterExt EXT
+  WriteRegStr HKCU "Software\Classes\SystemFileAssociations\${EXT}\shell\${APP_NAME}" "" "Convert with ${APP_NAME}"
+  WriteRegStr HKCU "Software\Classes\SystemFileAssociations\${EXT}\shell\${APP_NAME}" "Icon" "$INSTDIR\${EXE_NAME},0"
+  WriteRegStr HKCU "Software\Classes\SystemFileAssociations\${EXT}\shell\${APP_NAME}\command" "" '"$INSTDIR\${EXE_NAME}" -i "%1"'
+!macroend
+
+!macro UnregisterExt EXT
+  DeleteRegKey HKCU "Software\Classes\SystemFileAssociations\${EXT}\shell\${APP_NAME}"
+!macroend
+
+Section "ConvertGUI Application (Required)" SEC_APP
+  SectionIn RO
+  SetOutPath "$INSTDIR"
+  File "../dist/convert.exe"
+
+  WriteRegStr HKCU "Software\${APP_NAME}" "InstallDir" "$INSTDIR"
+  WriteUninstaller "$INSTDIR\uninstall.exe"
+
+  WriteRegStr HKCU "${UNINSTALL_REG}" "DisplayName" "${APP_NAME}"
+  WriteRegStr HKCU "${UNINSTALL_REG}" "DisplayVersion" "${VERSION}"
+  WriteRegStr HKCU "${UNINSTALL_REG}" "Publisher" "m4xx1m"
+  WriteRegStr HKCU "${UNINSTALL_REG}" "UninstallString" '"$INSTDIR\uninstall.exe"'
+  WriteRegStr HKCU "${UNINSTALL_REG}" "DisplayIcon" "$INSTDIR\${EXE_NAME},0"
+  WriteRegDWORD HKCU "${UNINSTALL_REG}" "NoModify" 1
+  WriteRegDWORD HKCU "${UNINSTALL_REG}" "NoRepair" 1
+
+  CreateDirectory "$SMPROGRAMS\${APP_NAME}"
+  CreateShortcut "$SMPROGRAMS\${APP_NAME}\${APP_NAME}.lnk" "$INSTDIR\${EXE_NAME}"
+  CreateShortcut "$SMPROGRAMS\${APP_NAME}\Uninstall ${APP_NAME}.lnk" "$INSTDIR\uninstall.exe"
+
+  ; Check Microsoft Edge WebView2 Runtime (required on older Windows 10)
+  SetRegView 32
+  ReadRegStr $0 HKLM "SOFTWARE\Microsoft\EdgeUpdate\Clients\{F3017226-FE2A-4295-8BDF-00C3A9A7E4C5}" "pv"
+  StrCmp $0 "" 0 webview2_done
+  ReadRegStr $0 HKCU "Software\Microsoft\EdgeUpdate\Clients\{F3017226-FE2A-4295-8BDF-00C3A9A7E4C5}" "pv"
+  StrCmp $0 "" 0 webview2_done
+  DetailPrint "Installing Microsoft Edge WebView2 Runtime..."
+  nsExec::ExecToLog 'powershell -NoProfile -ExecutionPolicy Bypass -Command "Invoke-WebRequest -Uri https://go.microsoft.com/fwlink/p/?LinkId=2124703 -OutFile $\'$TEMP\wv2setup.exe$\'; Start-Process $\'$TEMP\wv2setup.exe$\' -ArgumentList $\'/silent$\',$\'/install$\' -Wait; Remove-Item $\'$TEMP\wv2setup.exe$\' -ErrorAction SilentlyContinue"'
+  webview2_done:
+SectionEnd
+
+Section "Bundled FFmpeg & FFprobe" SEC_FFMPEG
+  SetOutPath "$INSTDIR\bin"
+  File "../dist/bin/ffmpeg.exe"
+  File "../dist/bin/ffprobe.exe"
+SectionEnd
+
+Section "Windows Explorer Context Menu" SEC_CTX
+  !insertmacro RegisterExt ".mp4"
+  !insertmacro RegisterExt ".mkv"
+  !insertmacro RegisterExt ".mov"
+  !insertmacro RegisterExt ".avi"
+  !insertmacro RegisterExt ".webm"
+  !insertmacro RegisterExt ".m4v"
+  !insertmacro RegisterExt ".flv"
+  !insertmacro RegisterExt ".ts"
+  !insertmacro RegisterExt ".wmv"
+SectionEnd
+
+Section "Desktop Shortcut" SEC_DESKTOP
+  CreateShortcut "$DESKTOP\${APP_NAME}.lnk" "$INSTDIR\${EXE_NAME}"
+SectionEnd
+
+LangString DESC_APP ${LANG_ENGLISH} "Core ConvertGUI application and Start Menu shortcut."
+LangString DESC_APP ${LANG_RUSSIAN} "Основное приложение ConvertGUI и ярлык в меню Пуск."
+LangString DESC_FFMPEG ${LANG_ENGLISH} "Standalone static FFmpeg & FFprobe binaries (recommended if not installed in PATH)."
+LangString DESC_FFMPEG ${LANG_RUSSIAN} "Встроенные FFmpeg и FFprobe (рекомендуется, если не установлены в PATH)."
+LangString DESC_CTX ${LANG_ENGLISH} "Add 'Convert with ConvertGUI' to Windows Explorer right-click menu for video files."
+LangString DESC_CTX ${LANG_RUSSIAN} "Добавить «Convert with ConvertGUI» в контекстное меню видеофайлов Проводника."
+LangString DESC_DESKTOP ${LANG_ENGLISH} "Create a shortcut on the Desktop."
+LangString DESC_DESKTOP ${LANG_RUSSIAN} "Создать ярлык на Рабочем столе."
+LangString MSG_RUNNING ${LANG_ENGLISH} "${APP_NAME} is currently running.$\r$\n$\r$\nClick OK to close it and proceed with the update, or Cancel to abort."
+LangString MSG_RUNNING ${LANG_RUSSIAN} "Приложение ${APP_NAME} сейчас запущено.$\r$\n$\r$\nНажмите ОК, чтобы закрыть его и продолжить обновление, или Отмена для выхода."
+
+Function .onInit
+  check_running:
+  nsExec::ExecToStack 'cmd /c tasklist /FI "IMAGENAME eq ${EXE_NAME}" | find /I "${EXE_NAME}"'
+  Pop $0
+  StrCmp $0 "0" 0 not_running
+    MessageBox MB_OKCANCEL|MB_ICONQUESTION $(MSG_RUNNING) IDOK close_it IDCANCEL abort_it
+    abort_it:
+      Abort
+    close_it:
+      nsExec::ExecToLog 'taskkill /F /IM ${EXE_NAME}'
+      Sleep 500
+      Goto check_running
+  not_running:
+FunctionEnd
+
+!insertmacro MUI_FUNCTION_DESCRIPTION_BEGIN
+  !insertmacro MUI_DESCRIPTION_TEXT ${SEC_APP} $(DESC_APP)
+  !insertmacro MUI_DESCRIPTION_TEXT ${SEC_FFMPEG} $(DESC_FFMPEG)
+  !insertmacro MUI_DESCRIPTION_TEXT ${SEC_CTX} $(DESC_CTX)
+  !insertmacro MUI_DESCRIPTION_TEXT ${SEC_DESKTOP} $(DESC_DESKTOP)
+!insertmacro MUI_FUNCTION_DESCRIPTION_END
+
+Section "Uninstall"
+  !insertmacro UnregisterExt ".mp4"
+  !insertmacro UnregisterExt ".mkv"
+  !insertmacro UnregisterExt ".mov"
+  !insertmacro UnregisterExt ".avi"
+  !insertmacro UnregisterExt ".webm"
+  !insertmacro UnregisterExt ".m4v"
+  !insertmacro UnregisterExt ".flv"
+  !insertmacro UnregisterExt ".ts"
+  !insertmacro UnregisterExt ".wmv"
+
+  Delete "$DESKTOP\${APP_NAME}.lnk"
+  RMDir /r "$SMPROGRAMS\${APP_NAME}"
+
+  Delete "$INSTDIR\bin\ffmpeg.exe"
+  Delete "$INSTDIR\bin\ffprobe.exe"
+  RMDir "$INSTDIR\bin"
+  Delete "$INSTDIR\${EXE_NAME}"
+  Delete "$INSTDIR\uninstall.exe"
+  RMDir "$INSTDIR"
+
+  DeleteRegKey HKCU "${UNINSTALL_REG}"
+  DeleteRegKey HKCU "Software\${APP_NAME}"
+SectionEnd

internal/config/config.go

@@ -0,0 +1,84 @@
+package config
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+)
+
+type AppConfig struct {
+	Language          string  `json:"language"` // "ru" or "en"
+	FFmpegPath        string  `json:"ffmpegPath"`
+	FFprobePath       string  `json:"ffprobePath"`
+	DefaultEncoder    string  `json:"defaultEncoder"` // libx264, h264_nvenc, libx265, hevc_nvenc
+	DefaultHwDecode   string  `json:"defaultHwDecode"`
+	DefaultPreset     string  `json:"defaultPreset"`
+	DefaultCRF        int     `json:"defaultCrf"`
+	DefaultFPS        int     `json:"defaultFps"` // 0 = original, 60 = 60fps
+	DefaultTune       string  `json:"defaultTune"`
+	DefaultMergeAudio bool    `json:"defaultMergeAudio"`
+	OutputSuffix      string  `json:"outputSuffix"`
+}
+
+func Default() AppConfig {
+	return AppConfig{
+		Language:          "ru",
+		DefaultEncoder:    "libx264",
+		DefaultHwDecode:   "none",
+		DefaultPreset:     "slow",
+		DefaultCRF:        20,
+		DefaultFPS:        60,
+		DefaultTune:       "film",
+		DefaultMergeAudio: true,
+		OutputSuffix:      "_converted",
+	}
+}
+
+func ConfigPath() (string, error) {
+	dir, err := os.UserConfigDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(dir, "ConvertGUI", "config.json"), nil
+}
+
+func Load() AppConfig {
+	cfg := Default()
+	path, err := ConfigPath()
+	if err != nil {
+		return cfg
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return cfg
+	}
+	_ = json.Unmarshal(data, &cfg)
+	if cfg.Language == "" {
+		cfg.Language = "ru"
+	}
+	if cfg.DefaultEncoder == "" {
+		cfg.DefaultEncoder = "libx264"
+	}
+	if cfg.DefaultPreset == "" {
+		cfg.DefaultPreset = "slow"
+	}
+	if cfg.DefaultCRF < 0 || cfg.DefaultCRF > 51 {
+		cfg.DefaultCRF = 20
+	}
+	return cfg
+}
+
+func Save(cfg AppConfig) error {
+	path, err := ConfigPath()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return err
+	}
+	data, err := json.MarshalIndent(cfg, "", "  ")
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(path, data, 0o644)
+}

internal/config/config_test.go

@@ -0,0 +1,42 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadDefaultsAndCRFClamp(t *testing.T) {
+	tmp := t.TempDir()
+	t.Setenv("APPDATA", tmp)
+	t.Setenv("XDG_CONFIG_HOME", tmp)
+
+	cfg := Default()
+	if cfg.DefaultCRF != 20 || cfg.DefaultPreset != "slow" || cfg.Language != "ru" {
+		t.Fatalf("unexpected defaults: %+v", cfg)
+	}
+
+	cfg.DefaultCRF = 99
+	if err := Save(cfg); err != nil {
+		t.Fatalf("save failed: %v", err)
+	}
+	loaded := Load()
+	if loaded.DefaultCRF != 20 {
+		t.Fatalf("expected invalid CRF 99 to reset to 20, got %d", loaded.DefaultCRF)
+	}
+
+	// CRF 0 (lossless) must be preserved
+	cfg.DefaultCRF = 0
+	if err := Save(cfg); err != nil {
+		t.Fatalf("save CRF 0 failed: %v", err)
+	}
+	loadedZero := Load()
+	if loadedZero.DefaultCRF != 0 {
+		t.Fatalf("expected CRF 0 to be preserved, got %d", loadedZero.DefaultCRF)
+	}
+
+	path, _ := ConfigPath()
+	if _, err := os.Stat(filepath.Clean(path)); err != nil {
+		t.Fatalf("config file missing: %v", err)
+	}
+}

internal/convert/command.go

@@ -0,0 +1,367 @@
+package convert
+
+import (
+	"fmt"
+	"math"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"convert/internal/media"
+)
+
+type CropRect struct {
+	Enabled bool `json:"enabled"`
+	X       int  `json:"x"`
+	Y       int  `json:"y"`
+	W       int  `json:"w"`
+	H       int  `json:"h"`
+}
+
+type Request struct {
+	InputPath      string   `json:"inputPath"`
+	OutputPath     string   `json:"outputPath"`
+	TrimStart      float64  `json:"trimStart"`
+	TrimEnd        float64  `json:"trimEnd"`
+	Encoder        string   `json:"encoder"`  // libx264, h264_nvenc, libx265, hevc_nvenc
+	HwDecode       string   `json:"hwDecode"` // none, nvdec, d3d11va, auto
+	Preset         string   `json:"preset"`
+	CRF            int      `json:"crf"`
+	Tune           string   `json:"tune"` // film, animation, grain, none
+	FPS            int      `json:"fps"`  // 0 = keep original
+	Speed          float64  `json:"speed"`
+	AudioMode      string   `json:"audioMode"` // merge, track, mute
+	AudioTrack     int      `json:"audioTrack"`
+	SelectedTracks []int    `json:"selectedTracks"`
+	Crop           CropRect `json:"crop"`
+	FastStart      bool     `json:"fastStart"`
+	Overwrite      bool     `json:"overwrite"`
+}
+
+type BuiltCommand struct {
+	Args             []string `json:"args"`
+	OutputPath       string   `json:"outputPath"`
+	ExpectedDuration float64  `json:"expectedDuration"`
+}
+
+func DefaultOutputPath(inputPath, suffix string) string {
+	if suffix == "" {
+		suffix = "_converted"
+	}
+	dir := filepath.Dir(inputPath)
+	base := strings.TrimSuffix(filepath.Base(inputPath), filepath.Ext(inputPath))
+	candidate := filepath.Join(dir, base+suffix+".mp4")
+	if strings.EqualFold(filepath.Clean(candidate), filepath.Clean(inputPath)) {
+		candidate = filepath.Join(dir, base+"_out.mp4")
+	}
+	return candidate
+}
+
+func formatCleanFloat(v float64) string {
+	rounded := math.Round(v*10000) / 10000
+	return strconv.FormatFloat(rounded, 'f', -1, 64)
+}
+
+func BuildAtempoChain(speed float64) []string {
+	if speed <= 0 || math.Abs(speed-1.0) < 0.001 {
+		return nil
+	}
+	var filters []string
+	rem := speed
+	for rem > 2.0+1e-6 {
+		filters = append(filters, "atempo=2")
+		rem /= 2.0
+	}
+	for rem < 0.5-1e-6 {
+		filters = append(filters, "atempo=0.5")
+		rem /= 0.5
+	}
+	if math.Abs(rem-1.0) >= 0.0001 {
+		filters = append(filters, "atempo="+formatCleanFloat(rem))
+	}
+	return filters
+}
+
+func BuildCommand(req Request, info *media.VideoInfo) (*BuiltCommand, error) {
+	if req.InputPath == "" {
+		return nil, fmt.Errorf("input path is required")
+	}
+	if info == nil {
+		return nil, fmt.Errorf("video info is required")
+	}
+	if req.TrimStart < 0 {
+		req.TrimStart = 0
+	}
+	if req.TrimEnd > 0 && req.TrimEnd <= req.TrimStart {
+		return nil, fmt.Errorf("trim end (%.2fs) must be greater than trim start (%.2fs)", req.TrimEnd, req.TrimStart)
+	}
+	if req.Speed <= 0 {
+		req.Speed = 1.0
+	}
+	if req.Speed < 0.25 || req.Speed > 8.0 {
+		return nil, fmt.Errorf("speed must be between 0.25x and 8.0x")
+	}
+	if req.CRF < 0 || req.CRF > 51 {
+		return nil, fmt.Errorf("CRF must be between 0 and 51")
+	}
+	if req.Encoder == "" {
+		req.Encoder = "libx264"
+	}
+	if req.Preset == "" {
+		req.Preset = "slow"
+	}
+
+	outPath := strings.TrimSpace(req.OutputPath)
+	if outPath == "" {
+		outPath = DefaultOutputPath(req.InputPath, "_converted")
+	}
+	if strings.EqualFold(filepath.Clean(outPath), filepath.Clean(req.InputPath)) {
+		return nil, fmt.Errorf("output path cannot be the same as input path")
+	}
+
+	args := []string{"-hide_banner"}
+	if req.Overwrite {
+		args = append(args, "-y")
+	} else {
+		args = append(args, "-n")
+	}
+
+	// Input hardware decode args
+	switch strings.ToLower(req.HwDecode) {
+	case "nvdec":
+		args = append(args, "-hwaccel", "nvdec", "-threads", "1")
+	case "d3d11va":
+		args = append(args, "-hwaccel", "d3d11va")
+	case "auto":
+		args = append(args, "-hwaccel", "auto")
+	}
+
+	// Trim before -i for fast seeking
+	if req.TrimStart > 0.001 {
+		args = append(args, "-ss", formatSeconds(req.TrimStart))
+	}
+	effectiveEnd := info.Duration
+	if req.TrimEnd > 0.001 && (info.Duration <= 0 || req.TrimEnd < info.Duration-0.01) {
+		args = append(args, "-to", formatSeconds(req.TrimEnd))
+		effectiveEnd = req.TrimEnd
+	}
+	if effectiveEnd <= req.TrimStart {
+		effectiveEnd = info.Duration
+	}
+	sourceClipDur := effectiveEnd - req.TrimStart
+	if sourceClipDur < 0 {
+		sourceClipDur = 0
+	}
+	expectedDur := sourceClipDur / req.Speed
+
+	args = append(args, "-i", req.InputPath)
+
+	// Video filters
+	var videoFilters []string
+	if req.Crop.Enabled && req.Crop.W > 0 && req.Crop.H > 0 {
+		cx := max(0, req.Crop.X)
+		cy := max(0, req.Crop.Y)
+		cw := req.Crop.W &^ 1
+		ch := req.Crop.H &^ 1
+		if cw < 2 {
+			cw = 2
+		}
+		if ch < 2 {
+			ch = 2
+		}
+		if info.Width > 0 && cx+cw > info.Width {
+			cw = (info.Width - cx) &^ 1
+		}
+		if info.Height > 0 && cy+ch > info.Height {
+			ch = (info.Height - cy) &^ 1
+		}
+		if cw >= 2 && ch >= 2 {
+			videoFilters = append(videoFilters, fmt.Sprintf("crop=%d:%d:%d:%d", cw, ch, cx, cy))
+		}
+	}
+
+	if math.Abs(req.Speed-1.0) >= 0.001 {
+		videoFilters = append(videoFilters, fmt.Sprintf("setpts=1/%s*PTS", formatCleanFloat(req.Speed)))
+	}
+
+	// Audio setup
+	numAudio := len(info.AudioStreams)
+	audioMode := strings.ToLower(req.AudioMode)
+	if audioMode == "" {
+		if numAudio > 1 {
+			audioMode = "merge"
+		} else {
+			audioMode = "track"
+		}
+	}
+	if numAudio == 0 {
+		audioMode = "mute"
+	}
+
+	var filterComplexParts []string
+	var postArgs []string
+
+	if len(videoFilters) > 0 {
+		filterComplexParts = append(filterComplexParts, "[0:v:0]"+strings.Join(videoFilters, ",")+"[v]")
+		postArgs = append(postArgs, "-map", "[v]")
+	} else {
+		postArgs = append(postArgs, "-map", "0:v:0")
+	}
+
+	atempoFilters := BuildAtempoChain(req.Speed)
+
+	switch audioMode {
+	case "mute":
+		postArgs = append(postArgs, "-an")
+	case "merge":
+		tracks := req.SelectedTracks
+		if tracks == nil {
+			for i := 0; i < numAudio; i++ {
+				tracks = append(tracks, i)
+			}
+		}
+		// Filter valid track indices
+		var validTracks []int
+		seen := map[int]bool{}
+		for _, idx := range tracks {
+			if idx >= 0 && idx < numAudio && !seen[idx] {
+				seen[idx] = true
+				validTracks = append(validTracks, idx)
+			}
+		}
+		if len(validTracks) == 0 {
+			postArgs = append(postArgs, "-an")
+		} else if len(validTracks) == 1 {
+			tIdx := validTracks[0]
+			if len(atempoFilters) > 0 {
+				filterComplexParts = append(filterComplexParts, fmt.Sprintf("[0:a:%d]%s[a]", tIdx, strings.Join(atempoFilters, ",")))
+				postArgs = append(postArgs, "-map", "[a]")
+			} else {
+				postArgs = append(postArgs, "-map", fmt.Sprintf("0:a:%d", tIdx))
+			}
+		} else {
+			var inputs strings.Builder
+			for _, tIdx := range validTracks {
+				inputs.WriteString(fmt.Sprintf("[0:a:%d]", tIdx))
+			}
+			chain := fmt.Sprintf("amix=inputs=%d:normalize=0", len(validTracks))
+			if len(atempoFilters) > 0 {
+				chain += "," + strings.Join(atempoFilters, ",")
+			}
+			filterComplexParts = append(filterComplexParts, inputs.String()+chain+"[a]")
+			postArgs = append(postArgs, "-map", "[a]")
+		}
+	default: // "track"
+		tIdx := req.AudioTrack
+		if tIdx < 0 || tIdx >= numAudio {
+			tIdx = 0
+		}
+		if len(atempoFilters) > 0 {
+			filterComplexParts = append(filterComplexParts, fmt.Sprintf("[0:a:%d]%s[a]", tIdx, strings.Join(atempoFilters, ",")))
+			postArgs = append(postArgs, "-map", "[a]")
+		} else {
+			postArgs = append(postArgs, "-map", fmt.Sprintf("0:a:%d", tIdx))
+		}
+	}
+
+	if len(filterComplexParts) > 0 {
+		args = append(args, "-filter_complex", strings.Join(filterComplexParts, ";"))
+	}
+	args = append(args, postArgs...)
+
+	// Video codec args
+	switch req.Encoder {
+	case "h264_nvenc":
+		args = append(args,
+			"-c:v", "h264_nvenc",
+			"-profile:v", "high",
+			"-pix_fmt", "yuv420p",
+			"-preset", mapNvencPreset(req.Preset),
+			"-rc", "vbr",
+			"-cq", strconv.Itoa(req.CRF),
+			"-b:v", "0",
+		)
+	case "libx265":
+		args = append(args,
+			"-c:v", "libx265",
+			"-pix_fmt", "yuv420p",
+			"-preset", req.Preset,
+			"-crf", strconv.Itoa(req.CRF),
+			"-tag:v", "hvc1",
+		)
+	case "hevc_nvenc":
+		args = append(args,
+			"-c:v", "hevc_nvenc",
+			"-pix_fmt", "yuv420p",
+			"-preset", mapNvencPreset(req.Preset),
+			"-rc", "vbr",
+			"-cq", strconv.Itoa(req.CRF),
+			"-b:v", "0",
+			"-tag:v", "hvc1",
+		)
+	default: // libx264
+		args = append(args,
+			"-c:v", "libx264",
+			"-profile:v", "high",
+			"-pix_fmt", "yuv420p",
+			"-preset", req.Preset,
+			"-crf", strconv.Itoa(req.CRF),
+		)
+		if req.Tune != "" && req.Tune != "none" {
+			args = append(args, "-tune", req.Tune)
+		}
+	}
+
+	if audioMode != "mute" {
+		args = append(args, "-c:a", "aac", "-b:a", "192k")
+	}
+
+	if req.FPS > 0 {
+		args = append(args, "-r", strconv.Itoa(req.FPS))
+	}
+
+	if req.FastStart {
+		args = append(args, "-movflags", "+faststart")
+	}
+
+	args = append(args, outPath)
+
+	return &BuiltCommand{
+		Args:             args,
+		OutputPath:       outPath,
+		ExpectedDuration: expectedDur,
+	}, nil
+}
+
+func mapNvencPreset(p string) string {
+	switch strings.ToLower(p) {
+	case "ultrafast", "superfast":
+		return "p1"
+	case "veryfast":
+		return "p2"
+	case "faster":
+		return "p3"
+	case "fast":
+		return "p4"
+	case "medium":
+		return "p5"
+	case "slow":
+		return "p6"
+	case "slower", "veryslow":
+		return "p7"
+	case "p1", "p2", "p3", "p4", "p5", "p6", "p7":
+		return p
+	default:
+		return "p6"
+	}
+}
+
+func formatSeconds(sec float64) string {
+	return strconv.FormatFloat(sec, 'f', 3, 64)
+}
+
+func EnsureUniqueOutputDir(outPath string) error {
+	dir := filepath.Dir(outPath)
+	return os.MkdirAll(dir, 0o755)
+}

internal/convert/command_test.go

@@ -0,0 +1,278 @@
+package convert
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"convert/internal/media"
+)
+
+func TestBuildAtempoChain(t *testing.T) {
+	if got := BuildAtempoChain(1.0); len(got) != 0 {
+		t.Fatalf("expected empty chain for 1.0, got %v", got)
+	}
+	got4 := BuildAtempoChain(4.0)
+	if len(got4) != 2 || got4[0] != "atempo=2" || got4[1] != "atempo=2" {
+		t.Fatalf("unexpected 4x chain: %v", got4)
+	}
+	gotQuarter := BuildAtempoChain(0.25)
+	if len(gotQuarter) != 2 || gotQuarter[0] != "atempo=0.5" || gotQuarter[1] != "atempo=0.5" {
+		t.Fatalf("unexpected 0.25x chain: %v", gotQuarter)
+	}
+}
+
+func TestBuildCommand_MultiAudioMergeAndTrim(t *testing.T) {
+	info := &media.VideoInfo{
+		Path:     `C:\videos\clip.mp4`,
+		Duration: 60,
+		Width:    1920,
+		Height:   1080,
+		AudioStreams: []media.AudioStream{
+			{Index: 1, AudioOrder: 0, Codec: "aac"},
+			{Index: 2, AudioOrder: 1, Codec: "aac"},
+		},
+	}
+	req := Request{
+		InputPath: `C:\videos\clip.mp4`,
+		TrimStart: 10,
+		TrimEnd:   30,
+		Encoder:   "libx264",
+		HwDecode:  "nvdec",
+		Preset:    "slow",
+		CRF:       20,
+		Tune:      "film",
+		FPS:       60,
+		Speed:     2.0,
+		AudioMode: "merge",
+		Crop:      CropRect{Enabled: true, X: 10, Y: 10, W: 1281, H: 721},
+		FastStart: true,
+		Overwrite: true,
+	}
+
+	built, err := BuildCommand(req, info)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if built.ExpectedDuration != 10 {
+		t.Fatalf("expected 10s output duration, got %v", built.ExpectedDuration)
+	}
+	joined := strings.Join(built.Args, " ")
+	for _, must := range []string{
+		"-hwaccel nvdec",
+		"-ss 10.000",
+		"-to 30.000",
+		"crop=1280:720:10:10",
+		"setpts=1/2*PTS",
+		"[0:a:0][0:a:1]amix=inputs=2:normalize=0,atempo=2[a]",
+		"-c:v libx264",
+		"-crf 20",
+		"-preset slow",
+		"-tune film",
+		"-r 60",
+		"-movflags +faststart",
+	} {
+		if !strings.Contains(joined, must) {
+			t.Fatalf("expected %q in args: %s", must, joined)
+		}
+	}
+}
+
+func TestBuildCommand_ValidationErrors(t *testing.T) {
+	info := &media.VideoInfo{Path: "a.mp4", Duration: 30}
+	if _, err := BuildCommand(Request{InputPath: "a.mp4", TrimStart: 20, TrimEnd: 10, Speed: 1}, info); err == nil {
+		t.Fatalf("expected error when trimEnd <= trimStart")
+	}
+	if _, err := BuildCommand(Request{InputPath: "a.mp4", OutputPath: "a.mp4", Speed: 1}, info); err == nil {
+		t.Fatalf("expected error when output == input")
+	}
+	if _, err := BuildCommand(Request{InputPath: "a.mp4", Speed: 12}, info); err == nil {
+		t.Fatalf("expected error for speed > 8.0")
+	}
+}
+
+func TestProgressParser(t *testing.T) {
+	p := newProgressParser(10.0)
+	lines := []string{
+		"fps=120.5",
+		"total_size=500000",
+		"out_time_us=5000000",
+		"speed=2.0x",
+		"progress=continue",
+	}
+	var got Progress
+	var ok bool
+	for _, l := range lines {
+		got, ok = p.feed(l)
+	}
+	if !ok {
+		t.Fatalf("expected progress completion on progress=continue")
+	}
+	if got.Percent != 50.0 {
+		t.Fatalf("expected 50%%, got %v", got.Percent)
+	}
+	if got.ETASec != 2.5 {
+		t.Fatalf("expected ETA 2.5s, got %v", got.ETASec)
+	}
+}
+
+func TestIntegration_RealFFmpegConvert(t *testing.T) {
+	bins := media.FindBinaries("", "")
+	if bins.FFmpeg == "" || bins.FFprobe == "" {
+		t.Skip("ffmpeg/ffprobe not installed on host")
+	}
+
+	tmpDir := t.TempDir()
+	src := filepath.Join(tmpDir, "source.mp4")
+	dst := filepath.Join(tmpDir, "out.mp4")
+
+	// Generate 4s synthetic test video with 2 audio tracks
+	gen := exec.Command(bins.FFmpeg,
+		"-hide_banner", "-loglevel", "error",
+		"-f", "lavfi", "-i", "testsrc=duration=4:size=640x360:rate=30",
+		"-f", "lavfi", "-i", "sine=frequency=440:duration=4",
+		"-f", "lavfi", "-i", "sine=frequency=880:duration=4",
+		"-map", "0:v", "-map", "1:a", "-map", "2:a",
+		"-c:v", "libx264", "-preset", "ultrafast", "-c:a", "aac", "-y", src,
+	)
+	if out, err := gen.CombinedOutput(); err != nil {
+		t.Fatalf("failed generating test video: %v (%s)", err, string(out))
+	}
+
+	info, err := media.Probe(bins.FFprobe, src)
+	if err != nil {
+		t.Fatalf("probe failed: %v", err)
+	}
+	if len(info.AudioStreams) != 2 {
+		t.Fatalf("expected 2 audio streams, got %d", len(info.AudioStreams))
+	}
+
+	built, err := BuildCommand(Request{
+		InputPath:  src,
+		OutputPath: dst,
+		TrimStart:  1.0,
+		TrimEnd:    3.0,
+		Encoder:    "libx264",
+		Preset:     "ultrafast",
+		CRF:        24,
+		FPS:        30,
+		Speed:      2.0,
+		AudioMode:  "merge",
+		Crop:       CropRect{Enabled: true, X: 10, Y: 10, W: 320, H: 180},
+		FastStart:  true,
+		Overwrite:  true,
+	}, info)
+	if err != nil {
+		t.Fatalf("BuildCommand failed: %v", err)
+	}
+
+	var lastProg Progress
+	runner := NewRunner()
+	if err := runner.Run(context.Background(), bins.FFmpeg, built, func(p Progress) {
+		lastProg = p
+	}); err != nil {
+		t.Fatalf("runner failed: %v", err)
+	}
+
+	if !lastProg.Done || lastProg.Percent != 100 {
+		t.Fatalf("expected Done=true and 100%%, got %+v", lastProg)
+	}
+	if _, err := os.Stat(dst); err != nil {
+		t.Fatalf("output missing: %v", err)
+	}
+
+	outInfo, err := media.Probe(bins.FFprobe, dst)
+	if err != nil {
+		t.Fatalf("probe output failed: %v", err)
+	}
+	if outInfo.Width != 320 || outInfo.Height != 180 {
+		t.Fatalf("expected cropped 320x180, got %dx%d", outInfo.Width, outInfo.Height)
+	}
+	if len(outInfo.AudioStreams) != 1 {
+		t.Fatalf("expected 1 merged audio stream, got %d", len(outInfo.AudioStreams))
+	}
+	if outInfo.Duration < 0.7 || outInfo.Duration > 1.4 {
+		t.Fatalf("expected ~1.0s duration after 2s clip @ 2x speed, got %v", outInfo.Duration)
+	}
+}
+
+func TestBuildCommand_EmptySelectedTracksMutes(t *testing.T) {
+	info := &media.VideoInfo{
+		Path:     `C:\videos\clip.mp4`,
+		Duration: 10,
+		Width:    1280,
+		Height:   720,
+		AudioStreams: []media.AudioStream{
+			{Index: 1, AudioOrder: 0, Codec: "aac"},
+			{Index: 2, AudioOrder: 1, Codec: "aac"},
+		},
+	}
+	built, err := BuildCommand(Request{
+		InputPath:      `C:\videos\clip.mp4`,
+		Encoder:        "libx264",
+		Preset:         "ultrafast",
+		CRF:            23,
+		Speed:          1.0,
+		AudioMode:      "merge",
+		SelectedTracks: []int{},
+	}, info)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	joined := strings.Join(built.Args, " ")
+	if !strings.Contains(joined, " -an ") {
+		t.Fatalf("expected -an when SelectedTracks is explicit empty slice, got: %s", joined)
+	}
+}
+
+func TestRunner_NoClobberPreservesExistingOutput(t *testing.T) {
+	bins := media.FindBinaries("", "")
+	if bins.FFmpeg == "" {
+		t.Skip("ffmpeg not installed on host")
+	}
+
+	tmpDir := t.TempDir()
+	src := filepath.Join(tmpDir, "source.mp4")
+	dst := filepath.Join(tmpDir, "existing.mp4")
+
+	gen := exec.Command(bins.FFmpeg,
+		"-hide_banner", "-loglevel", "error",
+		"-f", "lavfi", "-i", "testsrc=duration=1:size=320x180:rate=30",
+		"-c:v", "libx264", "-preset", "ultrafast", "-y", src,
+	)
+	if out, err := gen.CombinedOutput(); err != nil {
+		t.Fatalf("failed generating test video: %v (%s)", err, string(out))
+	}
+
+	sentinel := []byte("keep-me-intact")
+	if err := os.WriteFile(dst, sentinel, 0o644); err != nil {
+		t.Fatalf("write sentinel failed: %v", err)
+	}
+
+	info := &media.VideoInfo{Path: src, Duration: 1, Width: 320, Height: 180}
+	built, err := BuildCommand(Request{
+		InputPath:  src,
+		OutputPath: dst,
+		Encoder:    "libx264",
+		Preset:     "ultrafast",
+		CRF:        24,
+		Speed:      1.0,
+		AudioMode:  "mute",
+		Overwrite:  false,
+	}, info)
+	if err != nil {
+		t.Fatalf("BuildCommand failed: %v", err)
+	}
+
+	runner := NewRunner()
+	if err := runner.Run(context.Background(), bins.FFmpeg, built, nil); err == nil {
+		t.Fatalf("expected error when Overwrite=false and destination exists")
+	}
+	got, err := os.ReadFile(dst)
+	if err != nil || string(got) != string(sentinel) {
+		t.Fatalf("existing destination file was modified or deleted! err=%v got=%q", err, string(got))
+	}
+}

internal/convert/progress.go

@@ -0,0 +1,109 @@
+package convert
+
+import (
+	"strconv"
+	"strings"
+)
+
+type Progress struct {
+	Percent     float64 `json:"percent"`
+	OutTimeSec  float64 `json:"outTimeSec"`
+	TotalSec    float64 `json:"totalSec"`
+	FPS         float64 `json:"fps"`
+	Speed       string  `json:"speed"`
+	TotalSize   int64   `json:"totalSize"`
+	ETASec      float64 `json:"etaSec"`
+	Done        bool    `json:"done"`
+	Error       string  `json:"error,omitempty"`
+	OutputPath  string  `json:"outputPath,omitempty"`
+	OutputBytes int64   `json:"outputBytes,omitempty"`
+}
+
+type progressParser struct {
+	totalSec float64
+	current  Progress
+}
+
+func newProgressParser(totalSec float64) *progressParser {
+	return &progressParser{
+		totalSec: totalSec,
+		current: Progress{
+			TotalSec: totalSec,
+		},
+	}
+}
+
+// feed parses a single line from `ffmpeg -progress pipe:1` and returns (Progress, true) when a block completes.
+func (p *progressParser) feed(line string) (Progress, bool) {
+	line = strings.TrimSpace(line)
+	if line == "" {
+		return Progress{}, false
+	}
+	eq := strings.IndexByte(line, '=')
+	if eq <= 0 {
+		return Progress{}, false
+	}
+	key := strings.TrimSpace(line[:eq])
+	val := strings.TrimSpace(line[eq+1:])
+
+	switch key {
+	case "fps":
+		if v, err := strconv.ParseFloat(val, 64); err == nil {
+			p.current.FPS = v
+		}
+	case "total_size":
+		if v, err := strconv.ParseInt(val, 10, 64); err == nil && v >= 0 {
+			p.current.TotalSize = v
+		}
+	case "out_time_us":
+		if v, err := strconv.ParseInt(val, 10, 64); err == nil && v >= 0 {
+			p.current.OutTimeSec = float64(v) / 1_000_000.0
+		}
+	case "out_time_ms":
+		// Note: ffmpeg's out_time_ms is actually microseconds in many versions,
+		// so only use if out_time_us wasn't set.
+		if p.current.OutTimeSec == 0 {
+			if v, err := strconv.ParseInt(val, 10, 64); err == nil && v >= 0 {
+				p.current.OutTimeSec = float64(v) / 1_000_000.0
+			}
+		}
+	case "speed":
+		p.current.Speed = val
+	case "progress":
+		if p.totalSec > 0 {
+			pct := (p.current.OutTimeSec / p.totalSec) * 100.0
+			if pct > 100 {
+				pct = 100
+			}
+			if pct < 0 {
+				pct = 0
+			}
+			p.current.Percent = pct
+
+			if sp := parseSpeedFactor(p.current.Speed); sp > 0 && p.current.OutTimeSec < p.totalSec {
+				p.current.ETASec = (p.totalSec - p.current.OutTimeSec) / sp
+			} else {
+				p.current.ETASec = 0
+			}
+		}
+		if val == "end" {
+			p.current.Percent = 100
+			p.current.ETASec = 0
+			p.current.Done = true
+		}
+		return p.current, true
+	}
+	return Progress{}, false
+}
+
+func parseSpeedFactor(speedStr string) float64 {
+	s := strings.TrimSpace(strings.TrimSuffix(speedStr, "x"))
+	if s == "" || s == "N/A" {
+		return 0
+	}
+	v, err := strconv.ParseFloat(s, 64)
+	if err != nil || v <= 0 {
+		return 0
+	}
+	return v
+}

internal/convert/runner.go

@@ -0,0 +1,185 @@
+package convert
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+
+	"convert/internal/media"
+)
+
+type Runner struct {
+	mu     sync.Mutex
+	cancel context.CancelFunc
+	stdin  io.WriteCloser
+	active bool
+}
+
+func NewRunner() *Runner {
+	return &Runner{}
+}
+
+func (r *Runner) IsRunning() bool {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return r.active
+}
+
+func (r *Runner) Cancel() bool {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if !r.active {
+		return false
+	}
+	if r.stdin != nil {
+		_, _ = io.WriteString(r.stdin, "q\n")
+	}
+	if r.cancel != nil {
+		r.cancel()
+	}
+	return true
+}
+
+func (r *Runner) Run(
+	parentCtx context.Context,
+	ffmpegBin string,
+	built *BuiltCommand,
+	onProgress func(Progress),
+) error {
+	if ffmpegBin == "" {
+		return fmt.Errorf("ffmpeg binary not found")
+	}
+	if built == nil {
+		return fmt.Errorf("built command is nil")
+	}
+	if err := EnsureUniqueOutputDir(built.OutputPath); err != nil {
+		return fmt.Errorf("failed to create output directory: %w", err)
+	}
+
+	r.mu.Lock()
+	if r.active {
+		r.mu.Unlock()
+		return fmt.Errorf("conversion already in progress")
+	}
+	ctx, cancel := context.WithCancel(parentCtx)
+	r.cancel = cancel
+	r.active = true
+	r.mu.Unlock()
+
+	defer func() {
+		r.mu.Lock()
+		r.active = false
+		r.cancel = nil
+		r.stdin = nil
+		r.mu.Unlock()
+		cancel()
+	}()
+
+	args := append([]string{"-progress", "pipe:1", "-nostats"}, built.Args...)
+	cmd := exec.CommandContext(ctx, ffmpegBin, args...)
+	media.HideCmdWindow(cmd)
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	stdin, err := cmd.StdinPipe()
+	if err == nil {
+		r.mu.Lock()
+		r.stdin = stdin
+		r.mu.Unlock()
+	}
+
+	var stderrBuf bytes.Buffer
+	cmd.Stderr = &limitedBuffer{buf: &stderrBuf, max: 32 * 1024}
+
+	_, statErr := os.Stat(built.OutputPath)
+	existedBefore := statErr == nil
+	hasNoClobber := false
+	for _, a := range built.Args {
+		if a == "-n" {
+			hasNoClobber = true
+			break
+		}
+	}
+	if existedBefore && hasNoClobber {
+		return fmt.Errorf("output file already exists: %s", built.OutputPath)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("failed to start ffmpeg: %w", err)
+	}
+
+	parser := newProgressParser(built.ExpectedDuration)
+	scanner := bufio.NewScanner(stdout)
+	for scanner.Scan() {
+		if prog, ok := parser.feed(scanner.Text()); ok && onProgress != nil {
+			prog.OutputPath = built.OutputPath
+			onProgress(prog)
+		}
+	}
+
+	waitErr := cmd.Wait()
+	if ctx.Err() != nil {
+		if !(existedBefore && hasNoClobber) {
+			_ = os.Remove(built.OutputPath)
+		}
+		return fmt.Errorf("conversion cancelled")
+	}
+	if waitErr != nil {
+		if !(existedBefore && hasNoClobber) {
+			_ = os.Remove(built.OutputPath)
+		}
+		errTail := strings.TrimSpace(stderrBuf.String())
+		if len(errTail) > 800 {
+			errTail = errTail[len(errTail)-800:]
+		}
+		if errTail != "" {
+			return fmt.Errorf("ffmpeg error: %s", errTail)
+		}
+		return fmt.Errorf("ffmpeg failed: %w", waitErr)
+	}
+
+	var outSize int64
+	if st, err := os.Stat(built.OutputPath); err == nil {
+		outSize = st.Size()
+	}
+	if onProgress != nil {
+		onProgress(Progress{
+			Percent:     100,
+			OutTimeSec:  built.ExpectedDuration,
+			TotalSec:    built.ExpectedDuration,
+			TotalSize:   outSize,
+			OutputBytes: outSize,
+			OutputPath:  built.OutputPath,
+			Done:        true,
+		})
+	}
+	return nil
+}
+
+type limitedBuffer struct {
+	buf *bytes.Buffer
+	max int
+}
+
+func (l *limitedBuffer) Write(p []byte) (int, error) {
+	if l.buf.Len()+len(p) > l.max {
+		// keep latest tail
+		excess := l.buf.Len() + len(p) - l.max
+		if excess >= l.buf.Len() {
+			l.buf.Reset()
+		} else {
+			b := l.buf.Bytes()[excess:]
+			l.buf.Reset()
+			l.buf.Write(b)
+		}
+	}
+	return l.buf.Write(p)
+}

internal/media/bin.go

@@ -0,0 +1,84 @@
+package media
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+)
+
+type Binaries struct {
+	FFmpeg  string `json:"ffmpeg"`
+	FFprobe string `json:"ffprobe"`
+	Source  string `json:"source"` // "custom", "bundled", "path", "winget", "missing"
+}
+
+func FindBinaries(customFFmpeg, customFFprobe string) Binaries {
+	exeName := func(base string) string {
+		if runtime.GOOS == "windows" {
+			return base + ".exe"
+		}
+		return base
+	}
+
+	ff := findSingle(exeName("ffmpeg"), customFFmpeg)
+	fp := findSingle(exeName("ffprobe"), customFFprobe)
+
+	source := "missing"
+	if ff.path != "" && fp.path != "" {
+		source = ff.source
+	} else if ff.path != "" || fp.path != "" {
+		if ff.path != "" {
+			source = ff.source
+		} else {
+			source = fp.source
+		}
+	}
+
+	return Binaries{
+		FFmpeg:  ff.path,
+		FFprobe: fp.path,
+		Source:  source,
+	}
+}
+
+type foundBin struct {
+	path   string
+	source string
+}
+
+func findSingle(exeName, custom string) foundBin {
+	if custom != "" {
+		if st, err := os.Stat(custom); err == nil && !st.IsDir() {
+			return foundBin{path: custom, source: "custom"}
+		}
+	}
+
+	if exePath, err := os.Executable(); err == nil {
+		dir := filepath.Dir(exePath)
+		candidates := []string{
+			filepath.Join(dir, "bin", exeName),
+			filepath.Join(dir, exeName),
+		}
+		for _, c := range candidates {
+			if st, err := os.Stat(c); err == nil && !st.IsDir() {
+				return foundBin{path: c, source: "bundled"}
+			}
+		}
+	}
+
+	if p, err := exec.LookPath(exeName); err == nil {
+		return foundBin{path: p, source: "path"}
+	}
+
+	if runtime.GOOS == "windows" {
+		if localAppData := os.Getenv("LOCALAPPDATA"); localAppData != "" {
+			wg := filepath.Join(localAppData, "Microsoft", "WinGet", "Links", exeName)
+			if st, err := os.Stat(wg); err == nil && !st.IsDir() {
+				return foundBin{path: wg, source: "winget"}
+			}
+		}
+	}
+
+	return foundBin{}
+}

internal/media/exec_other.go

@@ -0,0 +1,9 @@
+//go:build !windows
+
+package media
+
+import "os/exec"
+
+func hideWindow(_ *exec.Cmd) {}
+
+func HideCmdWindow(_ *exec.Cmd) {}

internal/media/exec_windows.go

@@ -0,0 +1,19 @@
+//go:build windows
+
+package media
+
+import (
+	"os/exec"
+	"syscall"
+)
+
+func hideWindow(cmd *exec.Cmd) {
+	if cmd.SysProcAttr == nil {
+		cmd.SysProcAttr = &syscall.SysProcAttr{}
+	}
+	cmd.SysProcAttr.HideWindow = true
+}
+
+func HideCmdWindow(cmd *exec.Cmd) {
+	hideWindow(cmd)
+}

internal/media/probe.go

@@ -0,0 +1,228 @@
+package media
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+type AudioStream struct {
+	Index         int    `json:"index"`       // global stream index
+	AudioOrder    int    `json:"audioOrder"`  // 0-based audio track index (0:a:<order>)
+	Codec         string `json:"codec"`
+	Channels      int    `json:"channels"`
+	ChannelLayout string `json:"channelLayout"`
+	SampleRate    string `json:"sampleRate"`
+	Language      string `json:"language"`
+	Title         string `json:"title"`
+}
+
+type VideoInfo struct {
+	Path          string        `json:"path"`
+	FileName      string        `json:"fileName"`
+	Extension     string        `json:"extension"`
+	Container     string        `json:"container"`
+	SizeBytes     int64         `json:"sizeBytes"`
+	Duration      float64       `json:"duration"`
+	BitRate       int64         `json:"bitRate"`
+	Width         int           `json:"width"`
+	Height        int           `json:"height"`
+	FPS           float64       `json:"fps"`
+	VideoCodec    string        `json:"videoCodec"`
+	PixFmt        string        `json:"pixFmt"`
+	AudioStreams  []AudioStream `json:"audioStreams"`
+	BrowserNative bool          `json:"browserNative"`
+}
+
+type rawFFprobe struct {
+	Format struct {
+		Filename   string `json:"filename"`
+		FormatName string `json:"format_name"`
+		Duration   string `json:"duration"`
+		Size       string `json:"size"`
+		BitRate    string `json:"bit_rate"`
+	} `json:"format"`
+	Streams []struct {
+		Index         int               `json:"index"`
+		CodecType     string            `json:"codec_type"`
+		CodecName     string            `json:"codec_name"`
+		Width         int               `json:"width"`
+		Height        int               `json:"height"`
+		PixFmt        string            `json:"pix_fmt"`
+		AvgFrameRate  string            `json:"avg_frame_rate"`
+		RFrameRate    string            `json:"r_frame_rate"`
+		Channels      int               `json:"channels"`
+		ChannelLayout string            `json:"channel_layout"`
+		SampleRate    string            `json:"sample_rate"`
+		Duration      string            `json:"duration"`
+		Tags          map[string]string `json:"tags"`
+	} `json:"streams"`
+}
+
+func Probe(ffprobeBin, inputPath string) (*VideoInfo, error) {
+	if ffprobeBin == "" {
+		return nil, fmt.Errorf("ffprobe binary not found")
+	}
+	st, err := os.Stat(inputPath)
+	if err != nil {
+		return nil, fmt.Errorf("cannot access file: %w", err)
+	}
+	if st.IsDir() {
+		return nil, fmt.Errorf("path is a directory")
+	}
+
+	args := []string{
+		"-v", "quiet",
+		"-print_format", "json",
+		"-show_format",
+		"-show_streams",
+		inputPath,
+	}
+	cmd := exec.Command(ffprobeBin, args...)
+	hideWindow(cmd)
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("ffprobe failed: %w", err)
+	}
+
+	info, err := ParseProbeJSON(out, inputPath, st.Size())
+	if err != nil {
+		return nil, err
+	}
+	return info, nil
+}
+
+func ParseProbeJSON(data []byte, inputPath string, fileSize int64) (*VideoInfo, error) {
+	var raw rawFFprobe
+	if err := json.Unmarshal(data, &raw); err != nil {
+		return nil, fmt.Errorf("invalid ffprobe json: %w", err)
+	}
+
+	info := &VideoInfo{
+		Path:      inputPath,
+		FileName:  filepath.Base(inputPath),
+		Extension: strings.ToLower(filepath.Ext(inputPath)),
+		Container: raw.Format.FormatName,
+		SizeBytes: fileSize,
+	}
+
+	if d, err := strconv.ParseFloat(raw.Format.Duration, 64); err == nil && d > 0 {
+		info.Duration = d
+	}
+	if sz, err := strconv.ParseInt(raw.Format.Size, 10, 64); err == nil && sz > 0 {
+		info.SizeBytes = sz
+	}
+	if br, err := strconv.ParseInt(raw.Format.BitRate, 10, 64); err == nil && br > 0 {
+		info.BitRate = br
+	}
+
+	audioOrder := 0
+	hasVideo := false
+	for _, s := range raw.Streams {
+		switch s.CodecType {
+		case "video":
+			if !hasVideo {
+				hasVideo = true
+				info.Width = s.Width
+				info.Height = s.Height
+				info.VideoCodec = strings.ToLower(s.CodecName)
+				info.PixFmt = s.PixFmt
+				info.FPS = parseRationalFPS(s.AvgFrameRate)
+				if info.FPS <= 0 {
+					info.FPS = parseRationalFPS(s.RFrameRate)
+				}
+				if info.Duration <= 0 {
+					if d, err := strconv.ParseFloat(s.Duration, 64); err == nil && d > 0 {
+						info.Duration = d
+					}
+				}
+			}
+		case "audio":
+			lang := ""
+			title := ""
+			for k, v := range s.Tags {
+				lk := strings.ToLower(k)
+				if lk == "language" {
+					lang = v
+				} else if lk == "title" {
+					title = v
+				}
+			}
+			info.AudioStreams = append(info.AudioStreams, AudioStream{
+				Index:         s.Index,
+				AudioOrder:    audioOrder,
+				Codec:         strings.ToLower(s.CodecName),
+				Channels:      s.Channels,
+				ChannelLayout: s.ChannelLayout,
+				SampleRate:    s.SampleRate,
+				Language:      lang,
+				Title:         title,
+			})
+			audioOrder++
+		}
+	}
+
+	if !hasVideo {
+		return nil, fmt.Errorf("no video stream found in %s", filepath.Base(inputPath))
+	}
+
+	info.BrowserNative = isBrowserNative(info)
+	return info, nil
+}
+
+func parseRationalFPS(expr string) float64 {
+	expr = strings.TrimSpace(expr)
+	if expr == "" || expr == "0/0" {
+		return 0
+	}
+	parts := strings.Split(expr, "/")
+	if len(parts) == 1 {
+		v, err := strconv.ParseFloat(parts[0], 64)
+		if err != nil {
+			return 0
+		}
+		return v
+	}
+	if len(parts) == 2 {
+		num, err1 := strconv.ParseFloat(parts[0], 64)
+		den, err2 := strconv.ParseFloat(parts[1], 64)
+		if err1 != nil || err2 != nil || den == 0 {
+			return 0
+		}
+		return num / den
+	}
+	return 0
+}
+
+func IsH264BrowserNativePixFmt(pixFmt string) bool {
+	p := strings.ToLower(strings.TrimSpace(pixFmt))
+	return p == "" || p == "yuv420p" || p == "yuvj420p"
+}
+
+func isBrowserNative(info *VideoInfo) bool {
+	extOK := info.Extension == ".mp4" || info.Extension == ".m4v" || info.Extension == ".webm"
+	if !extOK {
+		return false
+	}
+	vOK := info.VideoCodec == "h264" || info.VideoCodec == "vp8" || info.VideoCodec == "vp9" || info.VideoCodec == "av1"
+	if !vOK {
+		return false
+	}
+	if info.VideoCodec == "h264" && !IsH264BrowserNativePixFmt(info.PixFmt) {
+		return false
+	}
+	// If multiple audio tracks exist, browser plays only track 0; if user wants to preview natively it's fine,
+	// we still treat single-compatible audio as native.
+	for _, a := range info.AudioStreams {
+		switch a.Codec {
+		case "aac", "mp3", "opus", "vorbis", "flac":
+		default:
+			return false
+		}
+	}
+	return true
+}

internal/media/probe_test.go

@@ -0,0 +1,129 @@
+package media
+
+import (
+	"testing"
+)
+
+func TestParseProbeJSON_MultiAudio(t *testing.T) {
+	sample := `{
+		"format": {
+			"filename": "clip.mp4",
+			"format_name": "mov,mp4,m4a,3gp,3g2,mj2",
+			"duration": "125.500000",
+			"size": "104857600",
+			"bit_rate": "6683824"
+		},
+		"streams": [
+			{
+				"index": 0,
+				"codec_type": "video",
+				"codec_name": "h264",
+				"width": 1920,
+				"height": 1080,
+				"pix_fmt": "yuv420p",
+				"avg_frame_rate": "60/1",
+				"r_frame_rate": "60/1"
+			},
+			{
+				"index": 1,
+				"codec_type": "audio",
+				"codec_name": "aac",
+				"channels": 2,
+				"channel_layout": "stereo",
+				"sample_rate": "48000",
+				"tags": {"title": "Desktop Audio"}
+			},
+			{
+				"index": 2,
+				"codec_type": "audio",
+				"codec_name": "aac",
+				"channels": 1,
+				"channel_layout": "mono",
+				"sample_rate": "48000",
+				"tags": {"title": "Microphone", "language": "rus"}
+			}
+		]
+	}`
+
+	info, err := ParseProbeJSON([]byte(sample), `C:\clips\clip.mp4`, 123)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if info.Width != 1920 || info.Height != 1080 {
+		t.Fatalf("unexpected resolution: %dx%d", info.Width, info.Height)
+	}
+	if info.FPS != 60 {
+		t.Fatalf("expected 60 fps, got %v", info.FPS)
+	}
+	if info.Duration != 125.5 {
+		t.Fatalf("expected duration 125.5, got %v", info.Duration)
+	}
+	if len(info.AudioStreams) != 2 {
+		t.Fatalf("expected 2 audio streams, got %d", len(info.AudioStreams))
+	}
+	if info.AudioStreams[1].AudioOrder != 1 || info.AudioStreams[1].Title != "Microphone" || info.AudioStreams[1].Language != "rus" {
+		t.Fatalf("unexpected audio stream 1: %+v", info.AudioStreams[1])
+	}
+	if !info.BrowserNative {
+		t.Fatalf("expected mp4 h264+aac to be browser native")
+	}
+}
+
+func TestParseProbeJSON_NoVideo(t *testing.T) {
+	sample := `{"format":{"duration":"10"},"streams":[{"index":0,"codec_type":"audio","codec_name":"mp3"}]}`
+	if _, err := ParseProbeJSON([]byte(sample), "audio.mp3", 100); err == nil {
+		t.Fatalf("expected error when no video stream exists")
+	}
+}
+
+func TestParseRationalFPS(t *testing.T) {
+	cases := []struct {
+		in   string
+		want float64
+	}{
+		{"60/1", 60},
+		{"30000/1001", 30000.0 / 1001.0},
+		{"0/0", 0},
+		{"", 0},
+		{"24", 24},
+	}
+	for _, tc := range cases {
+		got := parseRationalFPS(tc.in)
+		if got != tc.want {
+			t.Fatalf("parseRationalFPS(%q) = %v, want %v", tc.in, got, tc.want)
+		}
+	}
+}
+
+func TestParseProbeJSON_H264PixFmtCompatibility(t *testing.T) {
+	makeSample := func(pixFmt string) []byte {
+		return []byte(`{
+			"format": {"duration": "10.0"},
+			"streams": [{"index": 0, "codec_type": "video", "codec_name": "h264", "width": 1280, "height": 720, "pix_fmt": "` + pixFmt + `"}]
+		}`)
+	}
+
+	okInfo, err := ParseProbeJSON(makeSample("yuv420p"), "clip.mp4", 100)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !okInfo.BrowserNative {
+		t.Fatalf("expected yuv420p mp4 to be browser native")
+	}
+
+	hi10Info, err := ParseProbeJSON(makeSample("yuv420p10le"), "clip10.mp4", 100)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if hi10Info.BrowserNative {
+		t.Fatalf("expected 10-bit yuv420p10le mp4 NOT to be browser native")
+	}
+
+	fmt422Info, err := ParseProbeJSON(makeSample("yuv422p"), "clip422.mp4", 100)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if fmt422Info.BrowserNative {
+		t.Fatalf("expected yuv422p mp4 NOT to be browser native")
+	}
+}

internal/preview/server.go

@@ -0,0 +1,313 @@
+package preview
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha1"
+	"encoding/hex"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"convert/internal/media"
+)
+
+type Server struct {
+	addr       string
+	httpSrv    *http.Server
+	ctx        context.Context
+	cancel     context.CancelFunc
+	ffmpegBin  string
+	mu         sync.RWMutex
+	files      map[string]registeredFile
+	proxyLocks map[string]*sync.Mutex
+	proxyCache map[string]string
+	thumbCache map[string][]byte
+	tempFiles  []string
+}
+
+type registeredFile struct {
+	info *media.VideoInfo
+}
+
+func Start(ffmpegBin string) (*Server, error) {
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		return nil, err
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	s := &Server{
+		addr:       ln.Addr().String(),
+		ctx:        ctx,
+		cancel:     cancel,
+		ffmpegBin:  ffmpegBin,
+		files:      make(map[string]registeredFile),
+		proxyLocks: make(map[string]*sync.Mutex),
+		proxyCache: make(map[string]string),
+		thumbCache: make(map[string][]byte),
+	}
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/video", s.handleVideo)
+	mux.HandleFunc("/proxy", s.handleProxy)
+	mux.HandleFunc("/thumb", s.handleThumb)
+
+	s.httpSrv = &http.Server{
+		Handler:           mux,
+		ReadHeaderTimeout: 10 * time.Second,
+	}
+
+	go func() {
+		_ = s.httpSrv.Serve(ln)
+	}()
+
+	return s, nil
+}
+
+func (s *Server) SetFFmpeg(bin string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.ffmpegBin = bin
+}
+
+func (s *Server) BaseURL() string {
+	return "http://" + s.addr
+}
+
+func (s *Server) Register(info *media.VideoInfo) string {
+	var modUnix int64
+	if st, err := os.Stat(info.Path); err == nil {
+		modUnix = st.ModTime().UnixNano()
+	}
+	key := fmt.Sprintf("%s|%d|%d", info.Path, info.SizeBytes, modUnix)
+	sum := sha1.Sum([]byte(key))
+	id := hex.EncodeToString(sum[:8])
+
+	s.mu.Lock()
+	s.files[id] = registeredFile{info: info}
+	s.mu.Unlock()
+	return id
+}
+
+func (s *Server) Close() {
+	if s.cancel != nil {
+		s.cancel()
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	if s.httpSrv != nil {
+		_ = s.httpSrv.Shutdown(ctx)
+	}
+	s.mu.Lock()
+	for _, p := range s.tempFiles {
+		_ = os.Remove(p)
+	}
+	s.tempFiles = nil
+	s.mu.Unlock()
+}
+
+func (s *Server) getFile(id string) (registeredFile, bool) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	rf, ok := s.files[id]
+	return rf, ok
+}
+
+func (s *Server) handleVideo(w http.ResponseWriter, r *http.Request) {
+	id := r.URL.Query().Get("id")
+	rf, ok := s.getFile(id)
+	if !ok {
+		http.NotFound(w, r)
+		return
+	}
+	f, err := os.Open(rf.info.Path)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	defer f.Close()
+
+	st, err := f.Stat()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	http.ServeContent(w, r, rf.info.FileName, st.ModTime(), f)
+}
+
+func (s *Server) handleProxy(w http.ResponseWriter, r *http.Request) {
+	id := r.URL.Query().Get("id")
+	merge := r.URL.Query().Get("merge") == "1" || r.URL.Query().Get("merge") == "true"
+	rf, ok := s.getFile(id)
+	if !ok {
+		http.NotFound(w, r)
+		return
+	}
+
+	s.mu.RLock()
+	ffmpegBin := s.ffmpegBin
+	s.mu.RUnlock()
+	if ffmpegBin == "" {
+		http.Error(w, "ffmpeg not configured", http.StatusServiceUnavailable)
+		return
+	}
+
+	cacheKey := fmt.Sprintf("%s_m%v", id, merge)
+	s.mu.Lock()
+	lk, exists := s.proxyLocks[cacheKey]
+	if !exists {
+		lk = &sync.Mutex{}
+		s.proxyLocks[cacheKey] = lk
+	}
+	s.mu.Unlock()
+
+	lk.Lock()
+	defer lk.Unlock()
+
+	s.mu.RLock()
+	proxyPath := s.proxyCache[cacheKey]
+	s.mu.RUnlock()
+
+	if proxyPath == "" {
+		proxyPath = filepath.Join(os.TempDir(), fmt.Sprintf("convert_preview_%s.mp4", cacheKey))
+		if err := s.buildProxy(s.ctx, ffmpegBin, rf.info, merge, proxyPath); err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		s.mu.Lock()
+		s.proxyCache[cacheKey] = proxyPath
+		s.tempFiles = append(s.tempFiles, proxyPath)
+		s.mu.Unlock()
+	}
+
+	f, err := os.Open(proxyPath)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	defer f.Close()
+	st, err := f.Stat()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	http.ServeContent(w, r, "preview.mp4", st.ModTime(), f)
+}
+
+func (s *Server) buildProxy(ctx context.Context, ffmpegBin string, info *media.VideoInfo, merge bool, outPath string) error {
+	args := []string{"-hide_banner", "-loglevel", "error", "-y", "-i", info.Path}
+
+	numAudio := len(info.AudioStreams)
+	if numAudio == 0 {
+		args = append(args, "-map", "0:v:0", "-an")
+	} else if merge && numAudio > 1 {
+		var in strings.Builder
+		for i := 0; i < numAudio; i++ {
+			in.WriteString(fmt.Sprintf("[0:a:%d]", i))
+		}
+		args = append(args,
+			"-filter_complex", fmt.Sprintf("%samix=inputs=%d:normalize=0[a]", in.String(), numAudio),
+			"-map", "0:v:0", "-map", "[a]",
+			"-c:a", "aac", "-b:a", "128k",
+		)
+	} else {
+		args = append(args, "-map", "0:v:0", "-map", "0:a:0", "-c:a", "aac", "-b:a", "128k")
+	}
+
+	if info.VideoCodec == "h264" && media.IsH264BrowserNativePixFmt(info.PixFmt) {
+		// Remux video stream instantaneously when codec is already browser-native 8-bit H.264
+		args = append(args, "-c:v", "copy")
+	} else {
+		args = append(args,
+			"-c:v", "libx264",
+			"-preset", "ultrafast",
+			"-crf", "26",
+			"-pix_fmt", "yuv420p",
+			"-vf", "scale='min(1280,trunc(iw/2)*2)':-2",
+		)
+	}
+	args = append(args, "-movflags", "+faststart", outPath)
+
+	cmd := exec.CommandContext(ctx, ffmpegBin, args...)
+	media.HideCmdWindow(cmd)
+	var errBuf bytes.Buffer
+	cmd.Stderr = &errBuf
+	if err := cmd.Run(); err != nil {
+		_ = os.Remove(outPath)
+		return fmt.Errorf("preview proxy error: %v (%s)", err, strings.TrimSpace(errBuf.String()))
+	}
+	return nil
+}
+
+func (s *Server) handleThumb(w http.ResponseWriter, r *http.Request) {
+	id := r.URL.Query().Get("id")
+	tStr := r.URL.Query().Get("t")
+	rf, ok := s.getFile(id)
+	if !ok {
+		http.NotFound(w, r)
+		return
+	}
+	tSec, err := strconv.ParseFloat(tStr, 64)
+	if err != nil || tSec < 0 {
+		tSec = 0
+	}
+	if rf.info.Duration > 0 && tSec >= rf.info.Duration {
+		tSec = rf.info.Duration - 0.1
+		if tSec < 0 {
+			tSec = 0
+		}
+	}
+
+	key := fmt.Sprintf("%s_%.2f", id, tSec)
+	s.mu.RLock()
+	cached, found := s.thumbCache[key]
+	ffmpegBin := s.ffmpegBin
+	s.mu.RUnlock()
+
+	if !found {
+		if ffmpegBin == "" {
+			http.Error(w, "ffmpeg not configured", http.StatusServiceUnavailable)
+			return
+		}
+		cmd := exec.CommandContext(r.Context(), ffmpegBin,
+			"-hide_banner", "-loglevel", "error",
+			"-ss", strconv.FormatFloat(tSec, 'f', 3, 64),
+			"-i", rf.info.Path,
+			"-frames:v", "1",
+			"-vf", "scale=200:-1",
+			"-q:v", "6",
+			"-f", "image2pipe",
+			"-vcodec", "mjpeg",
+			"pipe:1",
+		)
+		media.HideCmdWindow(cmd)
+		data, err := cmd.Output()
+		if err != nil || len(data) == 0 {
+			http.Error(w, "thumbnail generation failed", http.StatusInternalServerError)
+			return
+		}
+		s.mu.Lock()
+		if len(s.thumbCache) > 200 {
+			// simple cap reset
+			s.thumbCache = make(map[string][]byte)
+		}
+		s.thumbCache[key] = data
+		s.mu.Unlock()
+		cached = data
+	}
+
+	w.Header().Set("Content-Type", "image/jpeg")
+	w.Header().Set("Cache-Control", "public, max-age=3600")
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	_, _ = w.Write(cached)
+}

internal/preview/server_test.go

@@ -0,0 +1,142 @@
+package preview
+
+import (
+	"io"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"convert/internal/media"
+)
+
+func TestPreviewServer_RangeThumbAndProxy(t *testing.T) {
+	bins := media.FindBinaries("", "")
+	if bins.FFmpeg == "" || bins.FFprobe == "" {
+		t.Skip("ffmpeg/ffprobe not installed")
+	}
+
+	tmpDir := t.TempDir()
+	src := filepath.Join(tmpDir, "clip.mkv")
+	gen := exec.Command(bins.FFmpeg,
+		"-hide_banner", "-loglevel", "error",
+		"-f", "lavfi", "-i", "testsrc=duration=2:size=320x180:rate=30",
+		"-f", "lavfi", "-i", "sine=frequency=440:duration=2",
+		"-c:v", "libx264", "-preset", "ultrafast", "-c:a", "aac", "-y", src,
+	)
+	if out, err := gen.CombinedOutput(); err != nil {
+		t.Fatalf("failed generating sample mkv: %v (%s)", err, string(out))
+	}
+
+	info, err := media.Probe(bins.FFprobe, src)
+	if err != nil {
+		t.Fatalf("probe failed: %v", err)
+	}
+
+	srv, err := Start(bins.FFmpeg)
+	if err != nil {
+		t.Fatalf("preview server start failed: %v", err)
+	}
+	defer srv.Close()
+
+	id := srv.Register(info)
+
+	// 1. Test Range request on /video
+	req, _ := http.NewRequest("GET", srv.BaseURL()+"/video?id="+id, nil)
+	req.Header.Set("Range", "bytes=0-127")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("GET /video failed: %v", err)
+	}
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusPartialContent {
+		t.Fatalf("expected 206 Partial Content, got %d", resp.StatusCode)
+	}
+
+	// 2. Test /thumb JPEG generation
+	tResp, err := http.Get(srv.BaseURL() + "/thumb?id=" + id + "&t=0.5")
+	if err != nil {
+		t.Fatalf("GET /thumb failed: %v", err)
+	}
+	tBody, _ := io.ReadAll(tResp.Body)
+	tResp.Body.Close()
+	if tResp.StatusCode != http.StatusOK || len(tBody) < 100 || tBody[0] != 0xFF || tBody[1] != 0xD8 {
+		t.Fatalf("expected valid JPEG thumbnail, status=%d len=%d", tResp.StatusCode, len(tBody))
+	}
+
+	// 3. Test /proxy MKV -> MP4 remux
+	pResp, err := http.Get(srv.BaseURL() + "/proxy?id=" + id + "&merge=0")
+	if err != nil {
+		t.Fatalf("GET /proxy failed: %v", err)
+	}
+	pBody, _ := io.ReadAll(pResp.Body)
+	pResp.Body.Close()
+	if pResp.StatusCode != http.StatusOK || len(pBody) < 500 {
+		t.Fatalf("expected valid MP4 proxy, status=%d len=%d", pResp.StatusCode, len(pBody))
+	}
+
+	// 4. Test unknown ID returns 404
+	nfResp, err := http.Get(srv.BaseURL() + "/video?id=nonexistent")
+	if err != nil {
+		t.Fatalf("GET /video 404 failed: %v", err)
+	}
+	nfResp.Body.Close()
+	if nfResp.StatusCode != http.StatusNotFound {
+		t.Fatalf("expected 404, got %d", nfResp.StatusCode)
+	}
+}
+
+func TestPreviewServer_CacheInvalidationAndOddWidthProxy(t *testing.T) {
+	bins := media.FindBinaries("", "")
+	if bins.FFmpeg == "" || bins.FFprobe == "" {
+		t.Skip("ffmpeg/ffprobe not installed")
+	}
+
+	tmpDir := t.TempDir()
+	src := filepath.Join(tmpDir, "odd.mkv")
+	// Odd width (321x180) vp8 source forces libx264 transcode in /proxy
+	gen := exec.Command(bins.FFmpeg,
+		"-hide_banner", "-loglevel", "error",
+		"-f", "lavfi", "-i", "testsrc=duration=1:size=321x180:rate=30",
+		"-c:v", "libvpx", "-y", src,
+	)
+	if out, err := gen.CombinedOutput(); err != nil {
+		t.Fatalf("failed generating odd-width mkv: %v (%s)", err, string(out))
+	}
+
+	info, err := media.Probe(bins.FFprobe, src)
+	if err != nil {
+		t.Fatalf("probe failed: %v", err)
+	}
+
+	srv, err := Start(bins.FFmpeg)
+	if err != nil {
+		t.Fatalf("start failed: %v", err)
+	}
+	defer srv.Close()
+
+	id1 := srv.Register(info)
+
+	// /proxy must succeed even on odd width (321 -> 320)
+	pResp, err := http.Get(srv.BaseURL() + "/proxy?id=" + id1 + "&merge=0")
+	if err != nil {
+		t.Fatalf("GET /proxy failed: %v", err)
+	}
+	pBody, _ := io.ReadAll(pResp.Body)
+	pResp.Body.Close()
+	if pResp.StatusCode != http.StatusOK || len(pBody) < 500 {
+		t.Fatalf("expected valid MP4 proxy for odd-width source, status=%d len=%d", pResp.StatusCode, len(pBody))
+	}
+
+	// Overwrite same path with different size -> Register must yield a new ID
+	if err := os.WriteFile(src, []byte("different-content-size"), 0o644); err != nil {
+		t.Fatalf("overwrite failed: %v", err)
+	}
+	info2 := *info
+	info2.SizeBytes = 22
+	id2 := srv.Register(&info2)
+	if id1 == id2 {
+		t.Fatalf("expected different videoId after file modification at same path, both were %q", id1)
+	}
+}

main.go

@@ -1,187 +1,75 @@
 package main
 
 import (
+	"embed"
 	"flag"
-	"fmt"
 	"os"
-	"os/exec"
+
-	"path/filepath"
+	"github.com/wailsapp/wails/v2"
-	"strconv"
+	"github.com/wailsapp/wails/v2/pkg/options"
-	"strings"
+	"github.com/wailsapp/wails/v2/pkg/options/assetserver"
-	"time"
+	"github.com/wailsapp/wails/v2/pkg/options/windows"
 )
 
-const DEFAULT_PRESET = "slow"
+// Version is injected at build time via -ldflags "-X main.Version=..."
-const DEFAULT_CRF = "20"
+var Version = "2.0.0-dev"
 
-func scanArgFromConsole(text string, v *string) error {
+//go:embed all:frontend/dist
-	fmt.Print(text)
+var assets embed.FS
-	if _, err := fmt.Scanln(v); err != nil && err.Error() == "EOF" {
+
-		return err
+func parseInitialFile(args []string) string {
+	fs := flag.NewFlagSet("convert", flag.ContinueOnError)
+	var input string
+	var debug bool
+	fs.StringVar(&input, "i", "", "input video path")
+	fs.BoolVar(&debug, "debug", false, "debug flag (ignored in GUI)")
+	_ = fs.Parse(args)
+	if input != "" {
+		return input
 	}
-	return nil
+	if fs.NArg() > 0 {
-}
+		return fs.Arg(0)
-
+	}
-func pressEnterToExit(code int) {
+	return ""
-	fmt.Print("\npress enter to exit... ")
-	_, _ = fmt.Scanln()
-	os.Exit(code)
 }
 
 func main() {
-	var err error
+	initialFile := parseInitialFile(os.Args[1:])
-	var debug bool
+	app := NewApp(initialFile)
-	var vfArgs []string
-	var audioFilters []string
-	var videoFilters []string
-	var inputVideo, ss, to, an, crf, preset, mergeAudioStreams, speedUp string
 
-	ffmpegExecutable := "ffmpeg"
+	err := wails.Run(&options.App{
-	ffmpegArgs := append(make([]string, 0, 30), "-hide_banner")
+		Title:     "ConvertGUI",
-	inputArgs := []string{
+		Width:     1240,
-		"-hwaccel", "nvdec",
+		Height:    840,
-		"-threads", "1",
+		MinWidth:  980,
-	}
+		MinHeight: 680,
-	postArgs := []string{
+		AssetServer: &assetserver.Options{
-		"-c:v", "h264",
+			Assets: assets,
-		"-profile:v", "high",
+		},
-		"-pix_fmt", "yuv420p",
+		BackgroundColour: &options.RGBA{R: 28, G: 28, B: 28, A: 1},
-		"-tune", "film",
+		Frameless:        true,
-		"-movflags", "+faststart",
+		OnStartup:        app.startup,
-		"-r", "60",
+		OnShutdown:       app.shutdown,
-	}
+		DragAndDrop: &options.DragAndDrop{
-
+			EnableFileDrop:     true,
-	flag.StringVar(&inputVideo, "i", "", "input video path")
+			DisableWebViewDrop: false,
-	flag.BoolVar(&debug, "debug", false, "debug mode (default params)")
+		},
-	flag.Parse()
+		Windows: &windows.Options{
-
+			WebviewIsTransparent:              false,
-	// check video exists
+			WindowIsTranslucent:               false,
-	if _, err := os.Stat(inputVideo); err != nil {
+			DisableFramelessWindowDecorations: true,
-		fmt.Println(err)
+			Theme:                             windows.Dark,
-		pressEnterToExit(1)
+			CustomTheme: &windows.ThemeSettings{
-	}
+				DarkModeTitleBar:  windows.RGB(37, 37, 37),
-
+				DarkModeTitleText: windows.RGB(212, 212, 212),
-	stat, err := ffprobe(inputVideo)
+				DarkModeBorder:    windows.RGB(56, 56, 56),
+			},
+		},
+		Bind: []interface{}{
+			app,
+		},
+	})
 	if err != nil {
-		fmt.Println(err)
+		println("Error:", err.Error())
-		return
-	}
-
-	if !debug {
-		err = func() error {
-			if err = scanArgFromConsole("ss > ", &ss); err != nil {
-				return err
-			}
-			if err = scanArgFromConsole("to > ", &to); err != nil {
-				return err
-			}
-			if err = scanArgFromConsole("an > ", &an); err != nil {
-				return err
-			}
-			if err = scanArgFromConsole(fmt.Sprintf("crf [%v] > ", DEFAULT_CRF), &crf); err != nil {
-				return err
-			}
-			if err = scanArgFromConsole("speed up > ", &speedUp); err != nil {
-				return err
-			}
-			if err = scanArgFromConsole(fmt.Sprintf("preset [%v] > ", DEFAULT_PRESET), &preset); err != nil {
-				return err
-			}
-			if err = scanArgFromConsole("merge audio streams > ", &mergeAudioStreams); err != nil {
-				return err
-			}
-			return nil
-		}()
-		if err != nil {
-			os.Exit(0)
-		}
-	}
-
-	for _, v := range []*string{&ss, &to, &an, &crf, &preset, &mergeAudioStreams, &speedUp} {
-		*v = strings.ToLower(strings.TrimSpace(*v))
-	}
-
-	if len(ss) != 0 {
-		inputArgs = append(inputArgs, "-ss", ss)
-	}
-
-	if len(to) != 0 {
-		inputArgs = append(inputArgs, "-to", to)
-	}
-
-	if len(an) != 0 {
-		postArgs = append(postArgs, "-an")
-	} else {
-		audioFilters = append(audioFilters, "amix=inputs=2:normalize=0")
-	}
-
-	if len(crf) == 0 {
-		crf = DEFAULT_CRF
-	}
-
-	if len(preset) == 0 {
-		preset = DEFAULT_PRESET
-	}
-
-	postArgs = append(postArgs, "-preset", preset)
-	postArgs = append(postArgs, "-crf", crf)
-
-	// speed up video and audio(?)
-	if len(speedUp) != 0 {
-		videoFilters = append(videoFilters, fmt.Sprintf("setpts=1/%s*PTS", speedUp))
-		if len(an) == 0 {
-			audioFilters = append(audioFilters, fmt.Sprintf("atempo=%s", speedUp))
-		}
-	}
-
-	if len(videoFilters) != 0 {
-		vfArgs = append(vfArgs, "[0:v:0]"+strings.Join(videoFilters, ",")+"[v]")
-		postArgs = append(postArgs, "-map", "[v]")
-	} else {
-		postArgs = append(postArgs, "-map", "0:v:0")
-	}
-
-	if len(audioFilters) != 0 {
-		vfArgs = append(vfArgs, "[0:a]"+strings.Join(audioFilters, ",")+"[a]")
-		postArgs = append(postArgs, "-map", "[a]")
-	} else {
-		postArgs = append(postArgs, "-map", "0:a")
-	}
-
-	// merge filter complex args
-	if len(vfArgs) != 0 {
-		postArgs = append(postArgs, "-filter_complex", strings.Join(vfArgs, ";"))
-	}
-
-	// out file name
-	outDir, _ := filepath.Split(inputVideo)
-	outFile := filepath.Join(outDir, strconv.FormatInt(time.Now().Unix(), 10)+".mp4")
-
-	// merge args to one slice
-	ffmpegArgs = append(ffmpegArgs, inputArgs...)
-	ffmpegArgs = append(ffmpegArgs, "-i", inputVideo)
-	ffmpegArgs = append(ffmpegArgs, postArgs...)
-	ffmpegArgs = append(ffmpegArgs, outFile)
-
-	fmt.Printf("
-running %v: %v
-
-", ffmpegExecutable, strings.Join(ffmpegArgs, " "))
-
-	proc := exec.Command(ffmpegExecutable, ffmpegArgs...)
-	proc.Stderr = os.Stderr
-	err = proc.Start()
-	if err != nil {
-		fmt.Println(err)
-		pressEnterToExit(1)
-	}
-	err = proc.Wait()
-	if err != nil {
-		fmt.Println(err)
-		pressEnterToExit(1)
-	}
-	if proc.ProcessState.ExitCode() != 0 {
-		fmt.Println(err)
-		pressEnterToExit(1)
 	}
 }

main_test.go

@@ -0,0 +1,18 @@
+package main
+
+import "testing"
+
+func TestParseInitialFile(t *testing.T) {
+	if got := parseInitialFile([]string{"-i", `C:\clips\demo.mp4`}); got != `C:\clips\demo.mp4` {
+		t.Fatalf("expected -i path, got %q", got)
+	}
+	if got := parseInitialFile([]string{"--debug", "-i", `E:\vid.mkv`}); got != `E:\vid.mkv` {
+		t.Fatalf("expected -i path with --debug, got %q", got)
+	}
+	if got := parseInitialFile([]string{`D:\drop.mov`}); got != `D:\drop.mov` {
+		t.Fatalf("expected positional path, got %q", got)
+	}
+	if got := parseInitialFile(nil); got != "" {
+		t.Fatalf("expected empty string, got %q", got)
+	}
+}

wails.json

@@ -0,0 +1,19 @@
+{
+  "$schema": "https://wails.io/schemas/config.v2.json",
+  "name": "ConvertGUI",
+  "outputfilename": "convert",
+  "frontend:install": "npm install",
+  "frontend:build": "npm run build",
+  "frontend:dev:watcher": "npm run dev",
+  "frontend:dev:serverUrl": "auto",
+  "author": {
+    "name": "m4xx1m"
+  },
+  "info": {
+    "companyName": "m4xx1m",
+    "productName": "ConvertGUI",
+    "productVersion": "2.0.0",
+    "copyright": "MIT",
+    "comments": "Fast FFmpeg GUI Video Converter with Preview and Trim"
+  }
+}