movenc: Adjust the pts of new fragments similarly to what is done for dts

The pts and the corresponding duration is written in sidx
atoms, thus make sure these match up correctly.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/movenc.c

@@ -3290,6 +3290,11 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
              * which might not exactly match our dts. Therefore adjust the dts
              * of this packet to be what the previous packets duration implies. */
             trk->cluster[trk->entry].dts = trk->start_dts + trk->track_duration;
+            /* We also may have written the pts and the corresponding duration
+             * in sidx tags; make sure the sidx pts and duration match up with
+             * the next fragment. This means the cts of the first sample must
+             * be the same in all fragments. */
+            pkt->pts = pkt->dts + trk->start_cts;
         } else {
             /* New fragment, but discontinuous from previous fragments.
              * Pretend the duration sum of the earlier fragments is
@@ -3331,6 +3336,9 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
         trk->flags |= MOV_TRACK_CTTS;
     trk->cluster[trk->entry].cts   = pkt->pts - pkt->dts;
     trk->cluster[trk->entry].flags = 0;
+    if (trk->start_cts == AV_NOPTS_VALUE)
+        trk->start_cts = pkt->pts - pkt->dts;
+
     if (enc->codec_id == AV_CODEC_ID_VC1) {
         mov_parse_vc1_frame(pkt, trk, mov->fragments);
     } else if (pkt->flags & AV_PKT_FLAG_KEY) {
@@ -3708,6 +3716,7 @@ static int mov_write_header(AVFormatContext *s)
          * this is updated. */
         track->hint_track = -1;
         track->start_dts  = AV_NOPTS_VALUE;
+        track->start_cts  = AV_NOPTS_VALUE;
         if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
             if (track->tag == MKTAG('m','x','3','p') || track->tag == MKTAG('m','x','3','n') ||
                 track->tag == MKTAG('m','x','4','p') || track->tag == MKTAG('m','x','4','n') ||

libavformat/movenc.h

@@ -104,6 +104,7 @@ typedef struct MOVTrack {
     uint32_t    tref_tag;
     int         tref_id; ///< trackID of the referenced track
     int64_t     start_dts;
+    int64_t     start_cts;
 
     int         hint_track;   ///< the track that hints this track, -1 if no hint track is set
     int         src_track;    ///< the track that this hint track describes