[Libav-user] Transcoding example produces incorrect FPS

[Tuukka Pasanen]

Hello,

Thanks this seems to solve problem. I didn't find this discussion with 
search engine. Nice explanation why number 512.

Ok I was assuming this was problem as I faced this with writing audio 
but when I debugged with ffmpeg.c this problem and it didn't set 
packet.duration and neither did transcoding.c but I assume it's been set 
just before writing to disk.

I update transcoding.c and try to make PR with it so nobody else 
shouldn't back head against wall with this.

Sincerely,

Tuukka


Vassilis kirjoitti 11.7.2020 klo 19.25:
> Hello,
>
> This seems like an issue I faced with my own attempt at transcoding 
> video and a fix was suggested by a member of this mailing list (thanks 
> James). You need to set the AVPacket duration field, otherwise this 
> issue is present. This would mean adding something in the lines of the 
> following line of code before your av_interleaved_write_frame is called:
>
> // for example, if 25 FPS, and time_base is 12800, then 
> packet.duration = 12800 / 25 = 512
> output_packet.duration = 
> format_context->streams[stream_index]->time_base.den / 
> format_context->streams[stream_index]->time_base.num / 
> format_context->streams[stream_index]->avg_frame_rate.num * 
> format_context->streams[stream_index]->avg_frame_rate.den;
>
>  /* mux encoded frame */
>     ret = av_interleaved_write_frame(format_context, output_packet);
>
> Hope this helps!
> Vas
>
> On Fri, Jul 10, 2020 at 9:19 PM Tuukka Pasanen 
> <pasanen.tuukka at gmail.com <mailto:pasanen.tuukka at gmail.com>> wrote:
>
>     Hello,
>
>     I noticed that example code 'doc/examples/transcoding.c' produces in
>     correct FPS if it's used with MP4 container. Encoded video type
>     doesn't
>     seem to be the case as I tested H264 and MPEG4 and both were nearly
>     identical.
>
>     With sort videos it's not much just something like 21,85 fps with
>     24 fps
>     video but longer ones can be something like 0.05 fps.
>
>     That it what ffprobe dump and when you play them they are really
>     lagging
>     as they go so slow. Packets seems to be correct and it neither
>     wise not
>     broken.
>
>     I don't know if this just feature or is this as bug. With ffmpeg same
>     source file produces correct file with correct fps.
>
>     Sincerely,
>
>     Tuukka
>
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