Re: [FFmpeg-devel] [PATCH 4/6] ffmpeg: don't skip packets before a keyframe was seen if a bsf with delay is used

[James Almer <jamrial@gmail.com>]

On 2/15/2022 8:41 AM, Anton Khirnov wrote:
> Quoting James Almer (2022-02-14 23:41:54)
>> A keyframe could be buffered in the bsf and not be output until more packets
>> had been fed to it.
>>
>> Signed-off-by: James Almer <jamrial@gmail.com>
>> ---
>>   fftools/ffmpeg.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
>> index 6aa0986f02..48d9016b4c 100644
>> --- a/fftools/ffmpeg.c
>> +++ b/fftools/ffmpeg.c
>> @@ -2026,7 +2026,8 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
>>       }
>>   
>>       if ((!ost->frame_number && !(pkt->flags & AV_PKT_FLAG_KEY)) &&
>> -        !ost->copy_initial_nonkeyframes)
>> +        !ost->copy_initial_nonkeyframes &&
>> +        !(ost->bsf_ctx && ost->bsf_ctx->filter->capabilities & AV_BSF_CAP_DELAY))
>>           return;
> 
> Wouldn't it be simpler to add an OutputStream field that tracks whether
> we've seen a keyframe packet yet? No new API required.

Probably. It would also only trigger when a keyframe was seen instead of 
unconditionally for all delay flagged bsfs.

I still think this new API is a good addition, either way. Only a 
handful of bsfs buffer packets and require the caller to flush them 
after sending NULL (av1_frame_merge, vp9_superframe, and setts after 
this set) so library users could have all this time never signaled EOF 
and never noticed anything wrong, much like it happened here.
The presence of this flag might help library users know they really need 
to signal EOF.
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