[Libav-user] Configuring mp4 muxer to not recalculate time_base to an absurd timescale value

[Charles Cross]

Hi Corey,

I also ran into the same issue upon moving to the 3.4 release. In my
application, I am muxing H264 Annex-B to mp4 from a custom AVIO input
context to a file output context.

I set the time_base value in the output AVStream to 1/90000, then stepped
through the code to write the header, some frames, and then the trailer.
Watching the time_base value in the debugger as I stepped through, I
noticed that the values change to the 1/15360 value after the invocation of
av_write_header(), which matches your findings. I am currently working
around the issue by rescaling each frame's PTS/DTS to the new 1/15360
timebase, rather than using the actual timebase associated with the stream
produced by the camera.

Would love to find out if there is a proper way to address this.

Cheers,
Charles

On Mon, Jan 8, 2018 at 8:48 PM, Corey Taylor <corey.taylor.fl at gmail.com>
wrote:

> >
> >         if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
> >            <snip>
> >
> >            if (mov->video_track_timescale) {
> >                 track->timescale = mov->video_track_timescale;
> >             } else {
> >                 track->timescale = st->time_base.den;
> >                 while(track->timescale < 10000)
> >                     track->timescale *= 2;
>
> This seems to be gated by FF_MOV_FLAG_RTP_HINT.
>
>     if (mov->flags & FF_MOV_FLAG_RTP_HINT) {
>         /* Add hint tracks for each audio and video stream */
>         for (i = 0; i < s->nb_streams; i++) {
>             AVStream *st = s->streams[i];
>             if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
>                 st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
>                 mov->nb_streams++;
>             }
>         }
>     }
>
>
> However, I can't seem to disable it.  The original code did not pass
> options to avformat_write_header() and didn't run into this.
>
> Are the track hints supposed to be created by default?
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