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

[James Almer]

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.

> 
> Carl Eugen
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