Re: [FFmpeg-devel] [PATCH 3/3] avformat/movenc: Add support for AVIF muxing

[Vignesh Venkatasubramanian <vigneshv-at-google.com@ffmpeg.org>]

On Thu, Mar 3, 2022 at 7:36 AM James Almer <jamrial@gmail.com> wrote:
>
> On 2/22/2022 6:43 PM, Vignesh Venkatasubramanian wrote:
> > Add an AVIF muxer by re-using the existing the mov/mp4 muxer.
> >
> > AVIF Specifiation: https://aomediacodec.github.io/av1-avif
> >
> > Sample usage for still image:
> > ffmpeg -i image.png -c:v libaom-av1 -avif-image 1 image.avif
> >
> > Sample usage for animated AVIF image:
> > ffmpeg -i video.mp4 animated.avif
> >
> > We can re-use any of the AV1 encoding options that will make
> > sense for image encoding (like bitrate, tiles, encoding speed,
> > etc).
> >
> > The files generated by this muxer has been verified to be valid
> > AVIF files by the following:
> > 1) Displays on Chrome (both still and animated images).
> > 2) Displays on Firefox (only still images, firefox does not support
> >     animated AVIF yet).
> > 3) Verfied to be valid by Compliance Warden:
> >     https://github.com/gpac/ComplianceWarden
> >
> > Fixes the encoder/muxer part of Trac Ticket #7621
> >
> > Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
> > ---
> >   configure                |   1 +
> >   libavformat/allformats.c |   1 +
> >   libavformat/movenc.c     | 300 +++++++++++++++++++++++++++++++++++----
> >   libavformat/movenc.h     |   5 +
> >   4 files changed, 282 insertions(+), 25 deletions(-)
>
> With a single frame i get no errors in that compliance tool, but when i
> encode an animated AVIF i get the following:
>
> [heif][Rule #12] Error: CodingConstraintsBox ('ccst') shall be present once
> [heif][Rule #28] Error: Wrong arity for boxes { ccst } in parents { avc1
> avc2 avc3 avc4 hev1 hev2 hvc1 hvc2 av01 }: expected in range [1-1], found 0
> [heif][Rule #31] Error: 'msf1' brand: this file shall conform to HEIF
> (section 7.2)
> [heif][Rule #31] Error: 'msf1' brand: 'iso8' shall be present among the
> compatible brands array
> [heif][Rule #32] Error: 'mif1' brand: this file shall conform to HEIF
> section 6, check the other errors for details
> [heif][Rule #33] Error: 'msf1' brand: this file shall conform to HEIF
> section 7, check the other errors for details
>
> All but one of these should be solved by writing a ccst box after the
> av1C box in the sample entry. The missing one should be solved by
> writing the iso8 compatible brand.
>
> The ccst box looks like it would need some bitstream information, so
> either you parse the packets to get it, or just hardcode sane defaults,
> considering it's used as a hint and it's not required for demuxing.

I recently fixed these errors in libavif [1][2] (the reference AVIF
encoder). I was hoping to have a follow-up patch since i already
uploaded the existing patches. Since you have pointed this out now, i
have included the fix in this patch itself. The new patch will now
write the iso8 compatible brand and the ccst box with sane default
values. The file produced is now identical to the file produced by
libavif in terms of box structure.

Also, notice that the compliance tool still shows the following error
for animated avif:

[avif][Rule #3] Warning: [ItemId=1] still_picture flag set to 0
[avif][Rule #4] Warning: [ItemId=1] reduced_still_picture_header flag set to 0

I believe these are incorrect since it does not make sense to set
these flag to 0 for animated avif sequences. These warnings also show
up with files produced by libavif. So it is okay to ignore them. I
will file an issue with the compliance tool separately.

Please take another look, thanks!

[1] https://github.com/AOMediaCodec/libavif/pull/855
[2] https://github.com/AOMediaCodec/libavif/pull/856
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-- 
Vignesh
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