[FFmpeg-devel] [PATCH v4] avformat/hls: Implement support for using AVSEEK_FLAG_BACKWARD when seeking

[Steven Liu]

Steven Liu <lq at chinaffmpeg.org> 于2022年2月3日周四 18:22写道：
>
>
>
> > 2022年1月29日 上午4:23，Gustav Grusell <gustav.grusell at gmail.com> 写道：
> >
> > Before, seeking in hls streams would always seek to the next keyframe
> > after the given timestamp. With this fix, if seeking in videostream and
> > AVSEEK_FLAG_BACKWARD is set, seeking will be to the first keyframe of
> > the segment containing the given timestamp. This fixes #7485.
> >
> > Signed-off-by: Gustav Grusell <gustav.grusell at gmail.com>
> > ---
> > libavformat/hls.c | 24 +++++++++++++++++-------
> > 1 file changed, 17 insertions(+), 7 deletions(-)
> >
> > diff --git a/libavformat/hls.c b/libavformat/hls.c
> > index 4568e72cb2..44afdaab42 100644
> > --- a/libavformat/hls.c
> > +++ b/libavformat/hls.c
> > @@ -1653,7 +1653,8 @@ static void add_metadata_from_renditions(AVFormatContext *s, struct playlist *pl
> > /* if timestamp was in valid range: returns 1 and sets seq_no
> >  * if not: returns 0 and sets seq_no to closest segment */
> > static int find_timestamp_in_playlist(HLSContext *c, struct playlist *pls,
> > -                                      int64_t timestamp, int64_t *seq_no)
> > +                                      int64_t timestamp, int64_t *seq_no,
> > +                                      int64_t *seg_start_ts)
> > {
> >     int i;
> >     int64_t pos = c->first_timestamp == AV_NOPTS_VALUE ?
> > @@ -1668,6 +1669,9 @@ static int find_timestamp_in_playlist(HLSContext *c, struct playlist *pls,
> >         int64_t diff = pos + pls->segments[i]->duration - timestamp;
> >         if (diff > 0) {
> >             *seq_no = pls->start_seq_no + i;
> > +            if (seg_start_ts) {
> > +                *seg_start_ts = pos;
> > +            }
> >             return 1;
> >         }
> >         pos += pls->segments[i]->duration;
> > @@ -1691,7 +1695,7 @@ static int64_t select_cur_seq_no(HLSContext *c, struct playlist *pls)
> >      * playlist) and this is a complete file, find the matching segment
> >      * by counting durations. */
> >     if (pls->finished && c->cur_timestamp != AV_NOPTS_VALUE) {
> > -        find_timestamp_in_playlist(c, pls, c->cur_timestamp, &seq_no);
> > +        find_timestamp_in_playlist(c, pls, c->cur_timestamp, &seq_no, NULL);
> >         return seq_no;
> >     }
> >
> > @@ -2362,7 +2366,7 @@ static int hls_read_seek(AVFormatContext *s, int stream_index,
> >     int i, j;
> >     int stream_subdemuxer_index;
> >     int64_t first_timestamp, seek_timestamp, duration;
> > -    int64_t seq_no;
> > +    int64_t seq_no, seg_start_ts;
> >
> >     if ((flags & AVSEEK_FLAG_BYTE) || (c->ctx->ctx_flags & AVFMTCTX_UNSEEKABLE))
> >         return AVERROR(ENOSYS);
> > @@ -2372,8 +2376,7 @@ static int hls_read_seek(AVFormatContext *s, int stream_index,
> >
> >     seek_timestamp = av_rescale_rnd(timestamp, AV_TIME_BASE,
> >                                     s->streams[stream_index]->time_base.den,
> > -                                    flags & AVSEEK_FLAG_BACKWARD ?
> > -                                    AV_ROUND_DOWN : AV_ROUND_UP);
> > +                                    AV_ROUND_DOWN);
> >
> >     duration = s->duration == AV_NOPTS_VALUE ?
> >                0 : s->duration;
> > @@ -2394,9 +2397,16 @@ static int hls_read_seek(AVFormatContext *s, int stream_index,
> >     }
> >     /* check if the timestamp is valid for the playlist with the
> >      * specified stream index */
> > -    if (!seek_pls || !find_timestamp_in_playlist(c, seek_pls, seek_timestamp, &seq_no))
> > +    if (!seek_pls || !find_timestamp_in_playlist(c, seek_pls, seek_timestamp, &seq_no, &seg_start_ts))
> >         return AVERROR(EIO);
> >
> > +    if (s->streams[stream_index]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
> > +        flags & AVSEEK_FLAG_BACKWARD && !(flags & AVSEEK_FLAG_ANY)) {
> > +        /* Seeking to start of segment ensures we seek to a keyframe located
> > +         * before the given timestamp. */
> > +        seek_timestamp = seg_start_ts;
> > +    }
> > +
> >     /* set segment now so we do not need to search again below */
> >     seek_pls->cur_seq_no = seq_no;
> >     seek_pls->seek_stream_index = stream_subdemuxer_index;
> > @@ -2423,7 +2433,7 @@ static int hls_read_seek(AVFormatContext *s, int stream_index,
> >
> >         if (pls != seek_pls) {
> >             /* set closest segment seq_no for playlists not handled above */
> > -            find_timestamp_in_playlist(c, pls, seek_timestamp, &pls->cur_seq_no);
> > +            find_timestamp_in_playlist(c, pls, seek_timestamp, &pls->cur_seq_no, NULL);
> >             /* seek the playlist to the given position without taking
> >              * keyframes into account since this playlist does not have the
> >              * specified stream where we should look for the keyframes */
> > --
> > 2.25.1
> >
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> >
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> >
>
> LGTM

Applied as e78d0810d1741535c95e5ae0f198977626b1cdff


Thanks
Steven