v0.1.12913 Aug 2026·Web APIs & DOM, Media

VP9 video in fragmented MP4 now actually plays, not just parses

Fragmented MP4 (ISO-BMFF) is the container almost every streaming site serves - DASH and a video site included. Floati learned to PARSE it a few releases ago, but nothing decoded: a VP9-in-MP4 clip produced no picture. Now it plays. The engine extracts the coded samples from each fragment (the moof/trun sample table pointing into mdat) and feeds them to the same royalty-free VP9 decoder that already drives WebM, producing real RGBA frames on the exact same <video> timeline. One decode entry point sniffs the container, so the <video> element and Media Source Extensions play WebM or MP4 without caring which. isTypeSupported now honestly answers yes to video/mp4 with VP9 (and VP8), and still no to H.264/avc1, HEVC, AV1 and MP4 audio, which have no clean-license decoder. Proven end to end on a real VP9-in-MP4 fixture decoding to 64x48 pixels. Media moves 40 to 41; overall holds at 52 (the patent-encumbered codecs most commercial streams use still do not play).

Parity with the reference browser

74overall, as of v0.1.343

Web APIs / DOM surface42

Security architecture66

GPU / graphics acceleration68

DevTools / extensions72

Networking85

Media85

Accessibility85

Real-world site compatibility99

HTML parsing100

CSS parsing + selectors100

Layout: block / flex / grid / tables / writing-modes100

Paint + visual100

JavaScript language100

JavaScript performance (JIT)100

HTML parsing100

What changed 3 changes

Web APIs & DOM	fMP4 sample extraction (core-demux/mp4.rs): full tfhd/tfdt/trun parse yields each coded sample as a byte range into mdat plus its decode/presentation time and sync flag, resolving offsets against the fragment base (base-data-offset or default-base-is-moof) and running contiguously by sample size. Two extraction tests against a real fixture (monotonic times, in-bounds ranges, per-fragment == whole-stream).
Media	VP9-in-MP4 decode (core-video): a container-aware entry point routes MP4 samples to the SAME libvpx VP9 decoder and RGBA path WebM uses, in presentation order, honoring the existing time/byte budgets. The <video> element's VideoTimeline plays it with no changes. Five end-to-end tests decode the fixture to real 64x48 RGBA frames.
Media	Honest capability reporting: MediaSource.isTypeSupported returns true for video/mp4 with vp09/vp08 only; avc1/hevc/av01 and any MP4 audio stay false (no clean-license decoder). Whole conformance suite unchanged (6375/6375).