[FFmpeg-devel] [PATCH] Fix segment muxer

[Marton Balint]

On Thu, 3 Oct 2019, just.one.man at yandex.ru wrote:

> It seems that my first attempt to send the patch failed (probably because my box where I executed "git send-email" failed reverse smtp check), so I'm going to re-send it to this same thread.
>
> ---
>
> When incoming media has non-zero start PTS,
> segment muxer would fail to correctly calculate
> the point where to chunk segments, as it always
> assumed that media starts with PTS==0.
>
> This change removes this assumption by remembering
> the PTS of the very first frame passed through the muxer.
>
> Also fix starting points of first segment
> ---
> libavformat/segment.c |   12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/segment.c b/libavformat/segment.c
> index e308206..2478d8f 100644
> --- a/libavformat/segment.c
> +++ b/libavformat/segment.c
> @@ -87,6 +87,7 @@ typedef struct SegmentContext {
>     int64_t last_val;      ///< remember last time for wrap around detection
>     int cut_pending;
>     int header_written;    ///< whether we've already called avformat_write_header
> +    int64_t start_pts;     ///< pts of the very first packet processed, used to compute correct segment length
>
>     char *entry_prefix;    ///< prefix to add to list entry filenames
>     int list_type;         ///< set the list type
> @@ -702,6 +703,7 @@ static int seg_init(AVFormatContext *s)
>         if ((ret = parse_frames(s, &seg->frames, &seg->nb_frames, seg->frames_str)) < 0)
>             return ret;
>     } else {
> +        seg->start_pts = -1;

AV_NOPTS_VALUE would be probably better for this purpose, even if the 
muxer won't get negative timestamps unless allowed by the 
AVFMT_TS_NEGATIVE flag.

Regards,
Marton

>         /* set default value if not specified */
>         if (!seg->time_str)
>             seg->time_str = av_strdup("2");
> @@ -914,7 +916,15 @@ calc_times:
>                 seg->cut_pending = 1;
>             seg->last_val = wrapped_val;
>         } else {
> -            end_pts = seg->time * (seg->segment_count + 1);
> +            if (seg->start_pts != -1) {
> +                end_pts = seg->start_pts + seg->time * (seg->segment_count + 1);
> +            } else if (pkt->stream_index == seg->reference_stream_index && pkt->pts != AV_NOPTS_VALUE) {
> +                // this is the first packet of the reference stream we see, initialize start point
> +                seg->start_pts = av_rescale_q(pkt->pts, st->time_base, AV_TIME_BASE_Q);
> +                seg->cur_entry.start_time = (double)pkt->pts * av_q2d(st->time_base);
> +                seg->cur_entry.start_pts = seg->start_pts;
> +                end_pts = seg->start_pts + seg->time * (seg->segment_count + 1);
> +            }
>         }
>     }
>
> --
> 1.7.9.5
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".