[FFmpeg-devel] [PATCH] lavf: consider codec timebase for framerate detection

[wm4]

On Tue, 30 May 2017 18:46:36 -0300
James Almer <jamrial at gmail.com> wrote:

> On 5/30/2017 9:07 AM, wm4 wrote:
> > On Tue, 23 May 2017 13:36:51 +0200
> > wm4 <nfxjfg at googlemail.com> wrote:
> >   
> >> Fixes detection of some TV sample as 24.5 FPS. With the patch applied,
> >> it's detected as 25 FPS.
> >> ---
> >>  libavformat/utils.c | 22 ++++++++++++++++++++++
> >>  1 file changed, 22 insertions(+)
> >>
> >> diff --git a/libavformat/utils.c b/libavformat/utils.c
> >> index fbd8b58ac2..778a82aeee 100644
> >> --- a/libavformat/utils.c
> >> +++ b/libavformat/utils.c
> >> @@ -3903,6 +3903,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
> >>                  st->info->codec_info_duration) {
> >>                  int best_fps      = 0;
> >>                  double best_error = 0.01;
> >> +                AVRational codec_frame_rate = av_inv_q(avctx->time_base);
> >>  
> >>                  if (st->info->codec_info_duration        >= INT64_MAX / st->time_base.num / 2||
> >>                      st->info->codec_info_duration_fields >= INT64_MAX / st->time_base.den ||
> >> @@ -3924,6 +3925,27 @@ FF_ENABLE_DEPRECATION_WARNINGS
> >>                          best_fps   = std_fps.num;
> >>                      }
> >>                  }
> >> +                if (avctx->ticks_per_frame > 0)
> >> +                    codec_frame_rate.num /= avctx->ticks_per_frame;
> >> +                for (j = 0; j < MAX_STD_TIMEBASES; j++) {
> >> +                    AVRational std_fps = { get_std_framerate(j), 12 * 1001 };
> >> +                    double error       = fabs(av_q2d(st->avg_frame_rate) /
> >> +                                              av_q2d(std_fps) - 1);
> >> +
> >> +                    if (error < best_error) {
> >> +                        best_error = error;
> >> +                        best_fps   = std_fps.num;
> >> +                    }
> >> +
> >> +                    if (codec_frame_rate.num > 0 && codec_frame_rate.den > 0) {
> >> +                        error       = fabs(av_q2d(codec_frame_rate) /
> >> +                                           av_q2d(std_fps) - 1);
> >> +                        if (error < best_error) {
> >> +                            best_error = error;
> >> +                            best_fps   = std_fps.num;
> >> +                        }
> >> +                    }
> >> +                }
> >>                  if (best_fps)
> >>                      av_reduce(&st->avg_frame_rate.num, &st->avg_frame_rate.den,
> >>                                best_fps, 12 * 1001, INT_MAX);  
> > 
> > Nobody wants to review this? It's pretty intrusive. I guess I'll push
> > tomorrow or so.  
> 
> According to the AVCodecContext->time_base doxy
> 
>      * - encoding: MUST be set by user.
>      * - decoding: the use of this field for decoding is deprecated.
>      *             Use framerate instead.
> 
> And it's scheduled to be dropped in the next bump (libav already did it).
> It's still used for decoding elsewhere in avformat_find_stream_info(),
> though, and even in other places, so this is probably going in the wrong
> direction and the other cases should be fixed instead.
> ffmpeg.c is apparently not using it for decoding, so that's good.
> 
> You may be able to use avctx->framerate for this. Check how the
> deprecated code in in lavc/utils.c and lavc/decode.c uses it to set
> avctx->time_base.

Right, the h264 decoder even sets the framerate field directly. I'll
see whether using that works.

Btw. what I really want is setting this as the framerate for mpegts,
any tips how to achieve this?