Patch ffmpeg to accept “dav1” codec tag for remuxing DV 10.0

[DrHurt]

What happened?

Looks like DV 10.0 remuxing isn’t working because ffmpeg doesn’t allow tag:v dav1 yet. This breaks AetherEngine’s ability to play such files on supported hardware.

I haven’t tested this myself as I don’t have AV1 compatible hardware yet but I’ve seen user reports saying it’s broken.

Proposed fix:
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20230315185711.4800-1-jamrial@gmail.com/

This will allow writing dav1 codec tag to init segments during remux

DV 10.1 and 10.4 use av01 which is supported by ffmpeg & works.

This only affect pure DV 10.0

Steps to reproduce

Play DV 10.0 file on an iPhone that supports HW AV1

AetherEngine version or commit SHA

All

Host app

Sodalite

Platform

iOS

OS version

27

Device / chip

iPhone 16 and newer

Playback path

Native AVPlayer

Source media (for playback bugs)

No response

Error codes / log lines

Anything else

No response

[superuser404notfound]

Thanks for the pointer, this was real and it was worse than the report: the tag is missing in two tables, not one, and the linked patch only covers the half that does not fix a remuxing player.

isom_tags.c is the read side. Without it a dav1 file cannot be opened at all. That is reproducible from public tools, no proprietary sample needed, since GPAC writes the tag the spec asks for:

ffmpeg -f lavfi -i testsrc=size=640x360:rate=24:duration=2 \
  -c:v libsvtav1 -pix_fmt yuv420p10le -color_primaries bt2020 \
  -color_trc smpte2084 -colorspace bt2020nc -f obu av1.obu
MP4Box -add "av1.obu:dvp=f10:stype=dav1" -new dv100.mp4
ffprobe dv100.mp4
# Video: none (dav1 / 0x31766164), none, 640x360
# Could not find codec parameters for stream 0: unknown codec

The write side is a second table, codec_mp4_tags in movenc.c, which is what validate_codec_tag() checks a requested tag against. Without a row there the tag resolves to 0 and avformat_write_header returns EINVAL, so the Profile 10.0 route never produced an init segment:

Tag dav1 incompatible with output codec id '225' (av01)
Could not write header (incorrect codec parameters ?)

dvh1 already sits in that second table for the HEVC side, which is exactly why Profile 5 works today and Profile 10.0 did not.

A second bug turned up next to it, and it was mine. Profile 10.1 was routed as a bare dav1 with no supplemental, which is the packaging of a source without a base layer. It has an HDR10-compatible one, so per the HLS authoring spec it belongs in an av01 sample entry with SUPPLEMENTAL-CODECS="dav1.10.XX/db1p" and VIDEO-RANGE=PQ, the same shape this engine already emitted for 10.4 with db4h and HLG. MP4Box makes the same split independently: dvp=f10 gets dav1, dvp=f10.hdr10 gets av01. So 10.1 was hitting the muxer refusal along with 10.0, for a reason that was not even the right packaging.

Shipped:

• FFmpegBuild 3.4.0, patch_ffmpeg_dav1_tag, one row in each table. Dav1CodecTagTests drives the shipped libavformat in both directions and was checked against 3.3.0's binaries, where both dav1 assertions fail and the av01 control still passes.
• AetherEngine 7.4.0 (659c24d), the pin plus the 10.1 packaging. Issue547AV1DolbyVisionRouteTests runs the real mp4 muxer with real av1C extradata: -22 against the old pin, 0 against the new one.
• Proposed upstream as PR 24556, with both halves. The 2023 patch on patchwork carried only the isom_tags.c line and was never applied.

Scope, since the report mentions tvOS and an iPhone: this only ever bit hosts with hardware AV1 decode (A17 Pro / M3 and newer). No Apple TV chip passes VTCapabilityProbe.av1Available, so there a Profile 10.0 source refuses with dolbyVisionRequiresHardware instead, which is deliberate and unchanged (IPT-PQ-c2 through dav1d renders green).

One honest gap: no device with hardware AV1 decode was available here, so what is measured is the muxer and the manifest, not AVPlayer accepting the served dav1 init segment. A retest on an A17 Pro or newer with a real Profile 10.0 file would close it. Leaving this open for that.

[DrHurt]

Sorry I wrote tvOS by mistake. I meant iOS & macOS with HW AV1 decode.

Hopefully a new Apple TV is coming soon though.

Looking forward to a real hardware test of this. It should work. I have an AV1 DV 10.0 mp4 test file (Dolby Reference material) but no HW to test it on. Edit: also an mkv.

I think I need a new MacBook 😅