The VP9 alpha encoding works correctly — verified by overlaying on a
green background with explicit VP9 decoder. FFmpeg's default decoder
doesn't expose VP9 alpha through ffprobe, but browsers and VP9-aware
decoders read it correctly.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- Force screenshot capture mode for WebM (beginFrame doesn't support
alpha channel in chrome-headless-shell)
- Set Emulation.setDefaultBackgroundColorOverride once during session
creation (matching experiment-framework's approach)
- Fix acquireBrowser to pass executable path in screenshot mode on
Linux (was setting undefined, causing puppeteer-core to fail)
- Add Page.captureScreenshot params: fromSurface, captureBeyondViewport,
optimizeForSpeed (matching experiment-framework)
- Fix regression harness extractMonoPcm16 for videos without audio
- Add getEncoderPreset unit tests
- Add webm-transparency regression test with golden baseline
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- New regression test `webm-transparency`: minimal transparent composition
rendered to WebM, validates VP9 codec and visual quality at 100
checkpoints against golden baseline
- Extend regression harness: `renderConfig.format` field ("mp4" | "webm"),
format-aware output paths and snapshot filenames
- Fix `extractMonoPcm16` to gracefully handle videos without audio
streams (WebM without audio was throwing instead of returning empty)
- Unit tests for `getEncoderPreset()`: VP9/yuva420p for WebM,
h264/yuv420p for MP4, preset mapping, quality preservation
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Miguel Ángel