Findings No. 4
MediaRecorder lossless is browser-specific, and Chrome's is nearly unreadable
Safari records ALAC in MP4; Chrome and Edge record raw PCM in WebM, which almost nothing opens. Pick from an isTypeSupported ladder and normalize server-side.
Ask MediaRecorder for lossless audio and you get a different answer per browser, one of them nearly useless. Safari 18.4 and later records ALAC in an MP4 container. Chrome and Edge 135 and later record raw PCM in WebM, a combination almost no software opens. A fresh WebM take also reports no duration, so any clock display has to use the timed length instead.
The working pattern: pick the first candidate that isTypeSupported accepts from a preference ladder, then normalize server-side. Our jobs function turns whatever the browser produced into FLAC, and the in-browser download path decodes the take and writes a 16-bit WAV so nobody receives a PCM-in-WebM file.
Receipt: Stem Shovel (utils/recordingMimeType.ts, commits 89a22db, 495ba61; the no-duration fix in 33d1973).