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atlas-iac/testing/fixtures/mediarecorder/SOURCE.md

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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.