AV1 stops shipping half a frame #95

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enricobuehler merged 2 commits from worktree-av1-subframe-truncation into main 2026-08-07 16:19:32 +00:00

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2 Commits

Author	SHA1	Message	Date
enricobuehler	6348334eff	docs(client/video): the evidence table stops saying AV1 never decoded ... Two of its notes became false the moment the host stopped truncating AV1. native D3D11VA / AV1 said "NEVER decoded a frame on any hardware". It has now decoded 4K60 on an RTX 3500 Ada — and the same run is why the note matters: its warn line named the rung as unproven moments before it failed 72 access units running with "reference picture N holds no DPB slot". That was the host shipping half of every frame, not the rung, so the M7 wiring was right all along. It stays UNVERIFIED regardless. `verified` gates `native_rung_admitted` — whether `auto` may pick this rung ahead of Vulkan Video — and one 25-second session with no frame-hash parity and no soak does not buy that. Promoting it wants a deliberate gpu_parity-style run. The note now says what is true instead of what is convenient. software / AV1 said rav1d had "CPU unit tests only". rav1d has now run on glass: 1080p AV1 decodes, and 4K ABORTS THE PROCESS. It takes an internal error path and panics inside its own on_error (rav1d 1.1.0 decode.rs:4997, unwrap on a None frame header); the panic crosses the extern "C" boundary in dav1d_send_data, so it is panic_cannot_unwind and no rung demotion or NoSoftwareRung refusal can catch it. libdav1d decodes the same 4K stream 715/715, so this is rav1d's own defect and is recorded where the next person to reach that rung will see it.	2026-08-07 17:06:35 +02:00
enricobuehler	c16e07d746	fix(encode/nvenc): AV1 stops shipping half a frame ... Every 4K AV1 frame this host encoded reached the wire truncated to its first tile, and had since AV1 was wired up. Measured on .21 (RTX 5070 Ti, 4K60, split AUTO): each access unit carried a frame header declaring two tile rows and a single Tile Group OBU with tg_start = tg_end = 0, so libdav1d rejected 835 of 836 AUs with "Error parsing frame header". NVIDIA's hardware decoder accepts the truncated stream, which is why native Vulkan Video looked healthy at 60 fps while both conformant software decoders — rav1d in-tree and libdav1d out-of-tree — refused every frame and clients fell to a black screen. The two halves of sub-frame readback are armed by different conditions. build_init_params arms the WRITER (enableSubFrameWrite + reportSliceOffsets) from subframe_on alone; the chunked READER additionally requires slices >= 2, and resolve_slices returns 1 for AV1 unconditionally — before the PUNKTFUNK_NVENC_SLICES override is even read, because AV1 partitions via tiles rather than slices. So an AV1 session asked the driver to publish its output tile by tile and then took only the first tile with one blocking lock_bitstream. resolve_split_subframe — the one arbitration point both direct-SDK backends already call — now disarms sub-frame for AV1 and returns split_mode untouched, so AV1 keeps every engine split encode gives it. Arming the reader instead is not a drop-in alternative: poll_chunk cuts at bitstreamSizeInBytes on the reasoning that "slices are contiguous Annex-B", which AV1's OBUs are not. With sub-frame disarmed and split still AUTO, the same session decodes 654/654 frames clean through libdav1d. The test that pinned this as correct (av1_untouched, "both features are legal together") is replaced by one that pins the disarm, and by one that checks the reader's gate against the writer's — the comparison nothing made. The Linux latch comment claiming the two "can't disagree" is corrected; that claim is what made this invisible.	2026-08-07 16:50:17 +02:00