[FFmpeg-devel] [PATCH v2 1/2] libavformat/utils: Interpolate missing timestamps in H264 and HEVC when no b-frames observed

[Michael Niedermayer]

On Tue, May 14, 2019 at 05:54:21PM -0400, Andriy Gelman wrote:
> From: Andriy Gelman <andriy.gelman at gmail.com>
> 
> Fixes Ticket #7895.
> 
> Currently, timestamp interpolation is disabled by default in H264 and
> HEVC.  This creates playback issues when the demuxer does not output a
> valid timestamp. This patch allows interpolation when no b-frames have
> been observed during decoding, which fixes playback issues for some
> missing timestamp cases.
> ---
>  libavformat/utils.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index a63d71b0f4..3dd0bf0d66 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -1233,7 +1233,9 @@ static void compute_pkt_fields(AVFormatContext *s, AVStream *st,
>      int64_t offset;
>      AVRational duration;
>      int onein_oneout = st->codecpar->codec_id != AV_CODEC_ID_H264 &&
> -                       st->codecpar->codec_id != AV_CODEC_ID_HEVC;
> +                       st->codecpar->codec_id != AV_CODEC_ID_HEVC ||
> +                       (!st->internal->avctx->max_b_frames &&
> +                        st->cur_dts != RELATIVE_TS_BASE); /*skip when no timing info from demuxer */
>  
>      if (s->flags & AVFMT_FLAG_NOFILLIN)
>          return;
> @@ -1272,6 +1274,10 @@ static void compute_pkt_fields(AVFormatContext *s, AVStream *st,
>      delay = st->internal->avctx->has_b_frames;
>      presentation_delayed = 0;
>  
> +    /*update max_b_frames if delay is larger */
> +    if (delay > st->internal->avctx->max_b_frames)
> +      st->internal->avctx->max_b_frames = delay;
> +
>      /* XXX: need has_b_frame, but cannot get it if the codec is
>       *  not initialized */
>      if (delay &&
> @@ -1337,7 +1343,8 @@ static void compute_pkt_fields(AVFormatContext *s, AVStream *st,
>              presentation_delayed, av_ts2str(pkt->pts), av_ts2str(pkt->dts), av_ts2str(st->cur_dts),
>              pkt->stream_index, pc, pkt->duration, delay, onein_oneout);
>  
> -    /* Interpolate PTS and DTS if they are not present. We skip H264
> +    /* Interpolate PTS and DTS if they are not present. H264/HEVC timestamps are
> +     * interpolated only if no b-frames have been observed. Otherwise, we skip H264/HEVC
>       * currently because delay and has_b_frames are not reliably set. */
>      if ((delay == 0 || (delay == 1 && pc)) &&
>          onein_oneout) {

This may produce some approximate values that are sometimes wrong.

If you want to compute exact timestamps, see "Conditional coding of timestamps"
in H.222. I only have a older draft here so mine only covers mpeg & h264 but 
maybe the next covers hevc too.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
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