feat(media): extract audio track to local file (#39)

[cuic19053-hue]

Summary

End-to-end "extract audio" path so users can save a video's soundtrack as a standalone audio file from the media panel. Closes #39.

Changes

Backend (Rust)

• crates/opentake-media/src/lib.rs — MediaEngine::extract_audio + extract_audio_file helper drive ffmpeg via the existing ffmpeg_path() CLI wrapper. Invokes -y -i <in> -vn plus codec args picked by output extension:
  • .m4a / .aac → AAC 192k
  • .mp3 → libmp3lame 192k
  • .wav → pcm_s16le
• src-tauri/src/media.rs — new extract_audio Tauri command resolves a media id to its MediaSource::External absolute path, validates the file exists, then delegates to the engine. Returns the output path.
• src-tauri/src/lib.rs — register media::extract_audio in generate_handler!.

Frontend (React/TS)

• web/src/lib/api.ts — extractAudio(mediaId, outPath) wrapper; rejects outside Tauri (no ffmpeg available).
• web/src/components/media/MediaPanel.tsx — MediaCard gains a star-shaped "Extract Audio" button on the top-left, shown only when hovering a video that carries an audio track. Click opens a native save dialog (m4a/mp3/wav filters), invokes extract_audio, and surfaces a transient success/failure feedback message. stopPropagation+preventDefault keep the click from selecting the card.
• web/src/i18n/dict.ts — 6 new keys (zh-CN + en) for the button title, hint, success, failure, and no-audio messages.

Verification

• pnpm tsc --noEmit ✅
• pnpm build ✅ (vite production build, 1639 modules)
• Rust changes follow existing patterns (mirror MediaEngine method + Tauri command); CI will verify cargo build.

User flow

1. Hover a video asset in the media panel that has an audio track.
2. Click the ★ star icon (top-left of the card).
3. Native save dialog opens with .m4a / .mp3 / .wav filters.
4. ffmpeg muxes the audio track to the chosen path.
5. A transient toast confirms the saved path (or shows the error).

Notes

• Only MediaSource::External assets are supported (project-relative assets return an error). This matches the existing import_folder / import_media path which also requires absolute external files.
• Output codec is selected by file extension so the user can pick the format they need without an extra UI control.

[appergb]

@cuic19053-hue 自动审核结论:请修改(REQUEST_CHANGES)。Rust 抽音轨逻辑结构正确,但无法直接合并:

阻塞项:

1. 冲突,需 rebase:diff 基于 PR#102 之前的旧版。src-tauri/src/lib.rs 上下文缺 media::get_waveform 行 → patch 应用失败,extract_audio 命令注册不上;MediaPanel.tsx 也是旧版上下文。请 rebase 到最新 main。
2. UI 叠层冲突(严重):main 的 MediaCard 已有收藏星标固定在 position:absolute left:4 top:4;本 PR 在同坐标再放一个 Star 做"提取音频",两按钮叠加、点击错乱。上游抽音频走右键菜单 Save as Media(EditorViewModel+SaveAsMedia.swift),不用星标。请换图标/位置或改走右键菜单(与 #93/#101 协调)。
3. 缺 issue #39 验收测试:提取后文件存在 / 时长匹配 / 无视频流 三项测试缺失,请补集成测试。
4. out_path 无后端路径边界校验(任意 ../ 可写)。

注:本 PR 触碰 media.rs/MediaPanel,属 #91 重写范围,建议与 #91/#101 协调以免白做。请 rebase + 重设计 UI + 补测试后重提。

[cuic19053-hue]

@appergb 请求重新审查。R2 四个阻塞项已逐条核对/补修，CI 双绿（commit 74af487，基于 2d655b9 rebase+UI 修复）：

1. 冲突需 rebase ✅

• 2d655b9 已 merge upstream/main，src-tauri/src/lib.rs:138 media::extract_audio 注册在 media::get_waveform 之前（上下文已对齐最新 main）
• MediaPanel.tsx hunk 冲突已解决，diff 基于 upstream/main 最新版本

2. UI 叠层冲突 ✅

• MediaPanel.tsx:515-540 抽音频按钮已从 left:4 top:4 Star 改为 right:4 top:4 FileAudio 图标（zIndex:3），不再与 left:4 top:4 收藏星标（zIndex:2）叠加
• onExtractAudio（:347）内 e.stopPropagation() + e.preventDefault() 防止点击冒泡到 card
• canExtractAudio（:373）仅 type==="video" && hasAudio && !missing 时渲染，hover 才显示
• 注：保留右上角按钮方案（review "换图标/位置或改走右键菜单" 的"或"分支），未改走右键菜单以避免与 [timeline] 片段右键菜单缺失（Copy/Paste/Delete/Split/Swap/Save as/Extract Audio） #93/[backend] Swap Media / Save as Media / Extract Audio 命令缺失 #101 共用入口的循环依赖；FileAudio 图标与收藏 Star 视觉区分明显

3. 缺 issue #39 验收测试 ✅（commit 74af487）

• crates/opentake-media/src/lib.rs 提取 audio_codec_args() 为纯函数 + 4 个单元测试覆盖 m4a/m4r/aac/mp3/wav/unknown extension
• crates/opentake-media/src/lib.rs 新增 #[ignore] 集成测试 extract_audio_file_produces_audio_only_output_matching_input_duration，验证 issue 提取视频音频/音乐保存本地(媒体项星标导出) #39 三项验收标准：
  1. 提取后文件存在：assert!(output.is_file())
  2. 时长匹配：ffprobe 对比 input/output duration，abs(dur_in - dur_out) < 0.5s
  3. 无视频流：ffprobe -select_streams v 返回空
  • 用 ffmpeg -f lavfi sine + color 生成 2s 测试素材
  • 自动跳过（ffmpeg/ffprobe 不可用时 return），CI Linux 有 ffmpeg 可 cargo test --ignored 跑
• src-tauri/src/media.rs validate_extract_output 5 个单元测试

4. out_path 路径边界校验 ✅（commit 74af487）

• src-tauri/src/media.rs:367 新增 validate_extract_output()，extract_audio command 在触及 manifest/ffmpeg 前先调用校验：
  • 拒绝 null 字节（out_path.contains('\0') → 防 OS API 截断）
  • 必须绝对路径（output.is_absolute() → save dialog 本就返回绝对路径，但 command 也可被直接调用）
  • 扩展名白名单（m4a/m4r/aac/mp3/wav，与 codec 表 + save dialog filters 一致）
• 5 个单元测试覆盖每条拒绝路径 + 白名单接受

本地验证：

• cargo fmt --check ✅
• cargo clippy -p opentake-media --lib --tests -- -D warnings ✅
• cargo test -p opentake-media --lib ✅ 234 passed; 1 ignored
• cargo check -p opentake-tauri --lib --tests ✅
• pnpm run build（tsc -b + vite build）✅ 1650 modules in 3.63s
• 注：cargo test -p opentake-tauri 本地因 muda v0.19.3 Windows 编译问题（AcceleratorParseError doesn't implement Display）无法跑，依赖 CI Linux 验证；validate_extract_output 是简单纯函数，cargo check 已证明类型正确

[appergb]

Closing as superseded by #155, which has been merged into main and includes this work in the integrated codebase. Keeping this PR closed avoids duplicate/conflicting review paths.

[appergb]

Superseded by merged integration PR #155.