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

[James Almer <jamrial@gmail.com>]

On 6/27/2022 1:43 PM, Vignesh Venkatasubramanian wrote:
> On Tue, Jun 21, 2022 at 10:12 AM Vignesh Venkatasubramanian
> <vigneshv@google.com> wrote:
>>
>> 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? :)
>>
> 
> Another ping on this please.
> 
>> --
>> Vignesh

I thought James Zern had push access, which is why i didn't apply it as 
soon as he reviewed it. Sorry.

Pushed it now.
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