# Chromium MediaRecorder fixture provenance

`chromium-webm-opus.webm` is the concatenation of ten successive 250 ms-ish
data blobs emitted by a real Chromium `MediaRecorder` for
`audio/webm;codecs=opus`; `chromium-webm-opus.json` records their exact byte
lengths so tests can replay each browser event. The recording has leading
silence followed by a 440 Hz signal, mirroring speech that begins after the
hands-free VAD pre-roll is full.

- Browser: Chromium 140.0.7339.16 (Playwright build v1187, arm64)
- Generator: `testing/probes/generate_mediarecorder_fixture.js`
- Timeslice request: 250 ms
- Complete concatenated payload: WebM/Opus, accepted by ffmpeg 7.1.5
- Complete payload SHA-256: `5585014ecad185511a727ccf47aa8b1ac70ea6f3efd7778309742bf88e6faf51`
- First five chunks are treated as pre-speech by the test model; the production
  pre-roll retains only the most recent three.

The fixture is generated data, not recorded speech.