Re: [FFmpeg-devel] [PATCH] avformat/movenc: Support alpha channel for AVIF

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

On Mon, Jun 13, 2022 at 10:17 AM James Zern
<jzern-at-google.com@ffmpeg.org> wrote:
>
> On Wed, Jun 1, 2022 at 11:06 AM Vignesh Venkatasubramanian
> <vigneshv-at-google.com@ffmpeg.org> wrote:
> >
> > AVIF specification allows for alpha channel as an auxiliary item (in
> > case of still images) or as an auxiliary track (in case of animated
> > images).  Add support for both of these. The AVIF muxer will take
> > exactly two streams (when alpha is present) as input (first one being
> > the YUV planes and the second one being the alpha plane).
> >
> > The input has to come from two different images (one of it color and
> > the other one being alpha), or it can come from a single file
> > source with the alpha channel extracted using the "alphaextract"
> > filter.
> >
> > Example using alphaextract:
> > ffmpeg -i rgba.png -filter_complex "[0:v]alphaextract[a]" -map 0 -map "[a]" -still-picture 1 avif_with_alpha.avif
> >
> > Example using two sources (first source can be in any pixel format and
> > the second source has to be in monochrome grey pixel format):
> > ffmpeg -i color.avif -i grey.avif -map 0 -map 1 -c copy avif_with_alpha.avif
> >
> > The generated files pass the compliance checks in Compliance Warden:
> > https://github.com/gpac/ComplianceWarden
> >
> > libavif (the reference avif library) is able to decode the files
> > generated using this patch.
> >
> > They also play back properly (with transparent background) in:
> > 1) Chrome
> > 2) Firefox (only still AVIF, no animation support)
> >
> > Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
> > ---
> >  libavformat/movenc.c | 188 +++++++++++++++++++++++++++++--------------
> >  libavformat/movenc.h |   4 +-
> >  2 files changed, 130 insertions(+), 62 deletions(-)
> >
>
> lgtm.
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Any more comments on this? If not can this be merged please? :)

-- 
Vignesh
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