[FFmpeg-devel] [PATCH] Fix segment muxer

[just.one.man at yandex.ru]

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..8b985df 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 = AV_NOPTS_VALUE;
         /* 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 != AV_NOPTS_VALUE) {
+                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

Now I tried to re-format as Nicolas George said, hopefully this is okay and won't make a third entry in patchwork (if it does - how do I stop it from doing so?)

07.10.2019, 15:15, "Nicolas George" <george at nsup.org>:
> just.one.man at yandex.ru (12019-10-07):
>>  Updated patch
>
> This should be after the triple dash, because it does not belong in the
> commit message.
>
>>  ---
>>
>>  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
>>  ---
>
> This should be before the triple dash, because it does belong in the
> commit message.
>
> I did not look at the code.
>
> Regards,
>
> --
>   Nicolas George
> ,
>
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