[FFmpeg-devel] [PATCH 1/1] avformat/mov: fix timecode with counter mode flag set

[Mark Reid]

On Sat, Nov 28, 2020 at 8:08 PM <mindmark at gmail.com> wrote:

> From: Mark Reid <mindmark at gmail.com>
>
> The current behaviour ends up squaring the avg_frame_rate if the conter
> mode flag is set.
> This messes up the timecode calculation, and looks to me as a regression
> that
> seems to have been introduced 428b4aac.
>
> The new behaviour is use the "Number of frames" field for avg_frame_rate
> from the timecode atom as describe here:
>
> https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html#//apple_ref/doc/uid/TP40000939-CH205-69831
>
> Number of frames
>     An 8-bit integer that contains the number of frames per second for the
> timecode format.
>     If the time is a counter, this is the number of frames for each
> counter tick.
>
> Here is a sample mov file with the counter flag set
> https://www.dropbox.com/s/5l4fucb9lhq523s/timecode_counter_mode.mov
>
> before the patch ffmpeg will report the timecode as:
> 00:37:11:97 and warns that the timecode framerate is 576000000/1002001
>
> after patch:
> 14:50:55:02
>
> ---
>  libavformat/mov.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 2b90e31170..76c1ceb82a 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -2336,24 +2336,17 @@ static int mov_parse_stsd_data(MOVContext *c,
> AVIOContext *pb,
>              tmcd_ctx->tmcd_flags = val;
>              st->avg_frame_rate.num = AV_RB32(st->codecpar->extradata +
> 8); /* timescale */
>              st->avg_frame_rate.den = AV_RB32(st->codecpar->extradata +
> 12); /* frameDuration */
> -#if FF_API_LAVF_AVCTX
> -FF_DISABLE_DEPRECATION_WARNINGS
> -            st->codec->time_base = av_inv_q(st->avg_frame_rate);
> -FF_ENABLE_DEPRECATION_WARNINGS
> -#endif
> +
>              /* adjust for per frame dur in counter mode */
>              if (tmcd_ctx->tmcd_flags & 0x0008) {
> -                int timescale = AV_RB32(st->codecpar->extradata + 8);
> -                int framedur = AV_RB32(st->codecpar->extradata + 12);
> -                st->avg_frame_rate.num *= timescale;
> -                st->avg_frame_rate.den *= framedur;
> +                st->avg_frame_rate.num = st->codecpar->extradata[16] /*
> fps, frames per counter tick in counter mode */;
> +                st->avg_frame_rate.den = 1;
> +            }
>  #if FF_API_LAVF_AVCTX
>  FF_DISABLE_DEPRECATION_WARNINGS
> -                st->codec->time_base.den *= timescale;
> -                st->codec->time_base.num *= framedur;
> +            st->codec->time_base = av_inv_q(st->avg_frame_rate);
>  FF_ENABLE_DEPRECATION_WARNINGS
>  #endif
> -            }
>              if (size > 30) {
>                  uint32_t len = AV_RB32(st->codecpar->extradata + 18); /*
> name atom length */
>                  uint32_t format = AV_RB32(st->codecpar->extradata + 22);
> --
> 2.29.2
>
>
ping