<video> / <audio> with only <source src> children skip extract and mix

[valeriangalliat]

Describe the bug

A <video> or <audio> that supplies its URL only via a child <source src> (no parent src) plays in preview and is skipped at export.

The runtime already resolves el.currentSrc || el.src. Engine extract and mix still query video[src] / audio[src], so those elements are never extracted or mixed. Lint media_missing_src agrees with the engine and tells you to put src on the parent.

Common HTML multi-format pattern. Parent src can stay preferred for Studio bind / variables; child <source> should still count as a resolvable src.

On 0.8.14 the skipped video is blank, not frozen. A native first-frame paint (frozen magenta) is the other face of the same skip — no frames extracted or injected. Audio is always missing.

Link to reproduction

https://github.com/ArcadeHQ/hyperframes-repros/tree/patch/video-source

Steps to reproduce

1. Clone https://github.com/ArcadeHQ/hyperframes-repros and check out patch/video-source.
2. Run npx hyperframes@latest check — media_missing_src on #source-only.
3. Run npx hyperframes@latest render --output renders/source-only.mp4.
4. Grab frames: ffmpeg -y -ss 0.3 -i renders/source-only.mp4 -frames:v 1 snapshots/frame-00-at-0.3s.png and the same at 1.5s.
5. Run ffprobe -hide_banner renders/source-only.mp4.

Same 2s clip twice (magenta 0–1s, cyan 1–2s, 440 Hz). Left: parent src, muted. Right: <source> only, audible.

Expected behavior

• t=0.3s: both panes magenta
• t=1.5s: both panes cyan
• Output has an audio stream (~440 Hz)

Actual behavior

• t=0.3s: left magenta; right black
• t=1.5s: left cyan; right still black
• ffprobe: video stream only — no audio
• Compile: videoCount: 1, audioCount: 0 with authoredTimedClipCount: 3

See snapshots/frame-00-at-0.3s.png and snapshots/frame-01-at-1.5s.png.

hyperframes snapshot (browser path) plays both panes. The gap is export.

Environment

hyperframes doctor

  ✓ Version          0.8.14 (latest)
  ✓ Node.js          v24.19.0 (darwin arm64)
  ✓ CPU              10 cores · Apple M1 Pro @ 2400MHz
  ✓ Memory           16.0 GB total · 4.9 GB available
  ✓ Disk             363.3 GB free
  ✓ Frames cache     /var/folders/bl/c4hk6r7n34g1d81txd99gsgr0000gn/T/hyperframes-extract-cache-501 · 363.3 GB free at /var/folders/bl/c4hk6r7n34g1d81txd99gsgr0000gn/T/hyperframes-extract-cache-501 · default
  ✓ Archive extractor unzip
  ✓ Environment      non-TTY
  ✗ whisper-cpp      Not found (optional — needed for transcription)
  ✗ TTS (Kokoro)     Not installed (optional — local voice fallback)
  ✗ BGM (MusicGen)   Not installed (optional — local music fallback)
  ✓ FFmpeg           ffmpeg 8.1.2 at /opt/homebrew/bin/ffmpeg
  ✓ FFprobe          ffprobe 8.1.2 at /opt/homebrew/bin/ffprobe
  ✓ Chrome           cache: /Users/val/.cache/puppeteer/chrome-headless-shell/mac_arm-152.0.7977.42/chrome-headless-shell-mac-arm64/chrome-headless-shell
  ✗ Docker           Not found
  ✗ Docker running   Not running

Additional context

Same over-narrow-selector family as tests/sub-composition-video and tests/video-hfid-no-id. Runtime half: mediaProxy.ts el.currentSrc || el.src.

Fix already in #3238 — this issue is so that PR can close it.