[FFmpeg-devel] [PATCH] avcodec/vp9_parser: export profile and pixel format

[James Almer]

On 10/29/2018 7:33 PM, Chris Cunningham wrote:
> Thanks for pushing the profile part. Turns out I'm also interested in
> pixel format, but I follow your comments about dropping the rest of
> patch. With the code as-is, how busted are we when parsing a super
> frame. Does it correctly grab the profile of the first frame?

It grabs the profile from the first frame in a super frame, which should
be safe since even if it's an invisible one it's not really going to be
different than the visible one, i think.

Also, when dealing with a super frame, to get other values like pixel
format and frame dimensions we'd have to make sure to parse the visible
frame, and if it's an inter frame also keep the reference frames around
to take said values from them.

> 
> Chrome actually has a fairly complete VP9 parser
> <https://cs.chromium.org/chromium/src/media/filters/vp9_parser.cc?rcl=adf255ef1da95255174643a6c1482e4305f877fd&l=478>
> but the CodecPrivate is no longer set in extradata for VP9 so we don't
> (AFAIK) have easy access to the frame header. Would you be open to
> surfacing codec private via extradata (reverting this change
> <http://ffmpeg.org/pipermail/ffmpeg-devel/2018-February/225548.html>)?

I don't think that change should be reverted, at least not without
further changes. Otherwise, WebM specific extradata (the one defined in
https://www.webmproject.org/docs/container) could make its way to other
containers. We'd have to add checks in supported muxers to ignore it
instead.

Also, what muxer currently writes that to CodecPrivate? I've looked at
Youtube samples and none has it.