[FFmpeg-devel] [PATCH] avformat/hls: fix seek accuracy problem

[Wu Zhiqiang]

On Wed, Jan 3, 2018 at 2:03 AM, Aman Gupta <ffmpeg at tmm1.net> wrote:

> On Tue, Jan 2, 2018 at 3:05 AM Steven Liu <lingjiujianke at gmail.com> wrote:
>
> > 2018-01-02 18:28 GMT+08:00  <mymoeyard at gmail.com>:
> > > From: Wu Zhiqiang <mymoeyard at gmail.com>
> > >
> > > HLS demuxer seeking use dts instead of pts.
> > > Demuxer skip some frame when dts is before pts in special case.
> > > And it is impossible to re-seek back to start time after playing.
> > > ---
> > >  libavformat/hls.c | 18 ++++++++++++++----
> > >  1 file changed, 14 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/libavformat/hls.c b/libavformat/hls.c
> > > index 950cc4c3bd..069e7b06e9 100644
> > > --- a/libavformat/hls.c
> > > +++ b/libavformat/hls.c
> > > @@ -2086,6 +2086,7 @@ static int hls_read_packet(AVFormatContext *s,
> > AVPacket *pkt)
> > >           * stream */
> > >          if (pls->needed && !pls->pkt.data) {
> > >              while (1) {
> > > +                int64_t pkt_ts;
> > >                  int64_t ts_diff;
> > >                  AVRational tb;
> > >                  ret = av_read_frame(pls->ctx, &pls->pkt);
> > > @@ -2101,9 +2102,17 @@ static int hls_read_packet(AVFormatContext *s,
> > AVPacket *pkt)
> > >                          fill_timing_for_id3_timestamped_stream(pls);
> > >                      }
> > >
> > > +                    if (pls->pkt.pts != AV_NOPTS_VALUE)
> > > +                        pkt_ts =  pls->pkt.pts;
> > > +                    else if (pls->pkt.dts != AV_NOPTS_VALUE)
> > > +                        pkt_ts =  pls->pkt.dts;
> > > +                    else
> > > +                        pkt_ts = AV_NOPTS_VALUE;
> > > +
> > > +
> > >                      if (c->first_timestamp == AV_NOPTS_VALUE &&
> > > -                        pls->pkt.dts       != AV_NOPTS_VALUE)
> > > -                        c->first_timestamp =
> av_rescale_q(pls->pkt.dts,
> > > +                        pkt_ts       != AV_NOPTS_VALUE)
> > > +                        c->first_timestamp = av_rescale_q(pkt_ts,
> > >                              get_timebase(pls), AV_TIME_BASE_Q);
> > >                  }
> > >
> > > @@ -2113,15 +2122,16 @@ static int hls_read_packet(AVFormatContext *s,
> > AVPacket *pkt)
> > >                  if (pls->seek_stream_index < 0 ||
> > >                      pls->seek_stream_index == pls->pkt.stream_index) {
> > >
> > > -                    if (pls->pkt.dts == AV_NOPTS_VALUE) {
> > > +                    if (pkt_ts == AV_NOPTS_VALUE) {
> > >                          pls->seek_timestamp = AV_NOPTS_VALUE;
> > >                          break;
> > >                      }
> > >
> > >                      tb = get_timebase(pls);
> > > -                    ts_diff = av_rescale_rnd(pls->pkt.dts,
> AV_TIME_BASE,
> > > +                    ts_diff = av_rescale_rnd(pkt_ts, AV_TIME_BASE,
> > >                                              tb.den, AV_ROUND_DOWN) -
> > >                              pls->seek_timestamp;
> > > +
> > >                      if (ts_diff >= 0 && (pls->seek_flags  &
> > AVSEEK_FLAG_ANY ||
> > >                                          pls->pkt.flags &
> > AV_PKT_FLAG_KEY)) {
> > >                          pls->seek_timestamp = AV_NOPTS_VALUE;
> > > --
> > > 2.15.0
> > >
> >
> >
> > LGTM , This patch can fix ticket : https://trac.ffmpeg.org/ticket/6850
> >
>
> LGTM, I've experienced this bug also.
>
>
> >
> > Thanks
> >
> > Steven
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel at ffmpeg.org
> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
I found another problem of seeking.
Example:http://devimages.apple.com.edgekey.net/
streaming/examples/bipbop_4x3/gear1/prog_index.m3u8,
return EIO error when seek to beginning.
Calculating first_timestamp only using first packet timestamp may cause
problem
when streams have each  different start time.
It is possible that second stream has smaller start time.
I try to fix it by using start_time of AVformatContext.
I am not not sure why not directly use start time.

Thanks