[FFmpeg-devel] [PATCH] avformat/hls:use EXT-X-START instead of live_start_index if it's in playlist

[Steven Liu]

<wolfleekay at gmail.com> 于2022年6月23日周四 23:01写道：
>
> From: Li Kai <wolfleekay at gmail.com>
Hi Li,
>
> Refer to https://datatracker.ietf.org/doc/html/rfc8216#section-4.3.5.2
>
> Signed-off-by: Li Kai <wolfleekay at gmail.com>
> ---
>  libavformat/hls.c | 68 ++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 62 insertions(+), 6 deletions(-)
>
> diff --git a/libavformat/hls.c b/libavformat/hls.c
> index 8204f55df3..96923c3eac 100644
> --- a/libavformat/hls.c
> +++ b/libavformat/hls.c
> @@ -120,6 +120,8 @@ struct playlist {
>      enum PlaylistType type;
>      int64_t target_duration;
>      int64_t start_seq_no;
> +    int time_offset_flag;
> +    int64_t start_time_offset;
>      int n_segments;
>      struct segment **segments;
>      int needed;
> @@ -741,6 +743,7 @@ static int parse_playlist(HLSContext *c, const char *url,
>      struct segment **prev_segments = NULL;
>      int prev_n_segments = 0;
>      int64_t prev_start_seq_no = -1;
> +    const char *p;
>
>      if (is_http && !in && c->http_persistent && c->playlist_pb) {
>          in = c->playlist_pb;
> @@ -889,6 +892,18 @@ static int parse_playlist(HLSContext *c, const char *url,
>                  cur_init_section->key = NULL;
>              }
>
> +        } else if (av_strstart(line, "#EXT-X-START:", &ptr)) {
> +            ret = ensure_playlist(c, &pls, url);
> +            if (ret < 0) {
> +                goto fail;
> +            }
> +            if (av_strstart(ptr, "TIME-OFFSET=", &p)) {
> +                float offset = strtof(p, NULL);
> +                pls->start_time_offset = offset * AV_TIME_BASE;
> +                pls->time_offset_flag = 1;
> +            } else {
> +                goto fail;
> +            }
This part is refine hls function, but i prefer reserved old process way bellow.
Support both way of them should be ok.
>          } else if (av_strstart(line, "#EXT-X-ENDLIST", &ptr)) {
>              if (pls)
>                  pls->finished = 1;
> @@ -1719,12 +1734,53 @@ static int64_t select_cur_seq_no(HLSContext *c, struct playlist *pls)
>               * require us to download a segment to inspect its timestamps. */
>              return c->cur_seq_no;
>
> -        /* If this is a live stream, start live_start_index segments from the
> -         * start or end */
> -        if (c->live_start_index < 0)
> -            return pls->start_seq_no + FFMAX(pls->n_segments + c->live_start_index, 0);
> -        else
> -            return pls->start_seq_no + FFMIN(c->live_start_index, pls->n_segments - 1);
> +        if (!pls->time_offset_flag) {
> +            /* If this is a live stream, start live_start_index segments from the
> +             * start or end */
> +            if (c->live_start_index < 0)
This could be set by user from command line.
It's not only used from play list, also can be controled by user.
> +                return pls->start_seq_no + FFMAX(pls->n_segments +
> +                                                c->live_start_index, 0);
> +            else
> +                return pls->start_seq_no + FFMIN(c->live_start_index,
> +                                                pls->n_segments - 1);
> +        } else {
> +            /* If playlist indicate a TIME-OFFSET, need to recalculate seq_no */
> +            int i;
> +            int64_t start_timestamp;
> +            int64_t playlist_duration = 0;
> +            int64_t cur_timestamp = c->cur_timestamp == AV_NOPTS_VALUE ? 0 :
> +                                    c->cur_timestamp;
> +
> +            for (i = 0; i < pls->n_segments; i++) {
> +                playlist_duration += pls->segments[i]->duration;
> +            }
> +            /* If the absolute value of TIME-OFFSET exceeds
> +             * the duration of the Playlist, it indicates either the end of the
> +             * Playlist (if positive) or the beginning of the Playlist (if
> +             * negative). */
> +            if (pls->start_time_offset >=0 &&
> +                pls->start_time_offset > playlist_duration)
> +                start_timestamp = cur_timestamp + playlist_duration;
> +            else if (pls->start_time_offset >= 0 &&
> +                        pls->start_time_offset <= playlist_duration)
> +                start_timestamp = cur_timestamp + pls->start_time_offset;
> +            else if (pls->start_time_offset < 0 &&
> +                        pls->start_time_offset < -playlist_duration)
> +                start_timestamp = cur_timestamp;
> +            else if (pls->start_time_offset < 0 &&
> +                        pls->start_time_offset > -playlist_duration)
> +                start_timestamp = cur_timestamp + playlist_duration +
> +                                    pls->start_time_offset;
> +            else
> +                start_timestamp = cur_timestamp;
> +
> +            find_timestamp_in_playlist(c, pls, start_timestamp, &seq_no, NULL);
> +            av_log(c, AV_LOG_DEBUG, "start_timestamp: %" PRId64
> +                                    "cur_timestamp:%" PRId64
> +                                    "cur_seq_no:%" PRId64 "\n",
> +                                    start_timestamp, cur_timestamp, seq_no);
> +            return seq_no;
> +        }
>      }
>
>      /* Otherwise just start on the first segment. */
> --
> 2.25.1
>
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Thanks
Steven