How the controlled codec capability list is produced
The capability table is neither a hand-written whitelist nor an extension rename. Five fixtures (three 10-second audio, two 5-second video) carry header bytes, declared MIME, ffprobe-equivalent probes (duration/channels/sample rate or width/height/fps), expected output and decode evidence.
verifyFixture() re-sniffs input and output headers, confirms the decoder/encoder is registered in the injectable codec registry, recomputes frame count/dimensions/duration and calls verifyOutput(). Any failure keeps the combination in rejected instead of open.
assertCombinationOpen() checks both the combination key and the option key: changing 480px/10fps to 640px/12fps returns UNVERIFIED_OPTIONS even for the same codec pair, because no controlled evidence exists. That is the testable "unverified combinations stay closed" rule.
Important boundary: no real ffmpeg.wasm, no ffprobe run and no browser decode this round. The capability list comes from controlled tests, not a real codec promise; the output is a text acceptance report, not playable media.