The harness's fMP4 push now sends what the OBS plugin sends with a "Music" stem: the fixture's audio as the full mix and as the stem, each in AAC and Opus, labeled through muxl's WithSegmentTrackMeta. CI runs the web stems spec with that push, and the Android Maestro suite runs on it so audio-stems.yaml executes; WHIP ingest stays covered by the main web run.