[FFmpeg-devel] [PATCH 3/3] avformat/webpenc: don't assume animated webp streams will have more than one packet

[Carl Eugen Hoyos]

Am So., 11. Apr. 2021 um 18:50 Uhr schrieb James Almer <jamrial at gmail.com>:
>
> On 4/11/2021 1:30 PM, Carl Eugen Hoyos wrote:
> > Am So., 11. Apr. 2021 um 04:13 Uhr schrieb James Almer <jamrial at gmail.com>:
> >>
> >> The libwebp_animencoder returns a single packet with the entire animated
> >> stream, as that's what the external library produces. As such, only ensure the
> >> stream was produced by said encoder (or propagated by a demuxer, once support
> >> is added) when attempting to write the requested loop value.
> >>
> >> Fixes ticket #9179.
> >>
> >> Signed-off-by: James Almer <jamrial at gmail.com>
> >> ---
> >>   libavformat/webpenc.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/libavformat/webpenc.c b/libavformat/webpenc.c
> >> index ed8325c02d..ca4ffc4e2d 100644
> >> --- a/libavformat/webpenc.c
> >> +++ b/libavformat/webpenc.c
> >> @@ -172,7 +172,7 @@ static int webp_write_trailer(AVFormatContext *s)
> >>       WebpContext *w = s->priv_data;
> >>
> >>       if (w->using_webp_anim_encoder) {
> >> -        if ((w->frame_count > 1) && w->loop) {  // Write loop count.
> >> +        if (w->loop) {  // Write loop count.
> >>               avio_seek(s->pb, 42, SEEK_SET);
> >>               avio_wl16(s->pb, w->loop);
> >
> > Sorry for not understanding this:
> > Why is the seek necessary at all?
>
> If we write the loop value in webp_write_trailer() then there's no other
> way. But if we instead attempt to write it in webp_write_packet() then a
> seek wouldn't be needed, no.

If I don't miss anything, the value should not be written in
webp_write_trailer() then.

Carl Eugen