movdec: fix dts generation in fragmented files

Do not use AVStream's duration for dts generation since it contains in
some cases the duration of the whole file instead of duration of the
samples in the moov. This happens if the mdhd holds the duration of the
whole file but has no entries or a zero duration in its stts.

libavformat/isom.h

@@ -126,6 +126,7 @@ typedef struct MOVStreamContext {
     uint32_t palette[256];
     int has_palette;
     int64_t data_size;
+    int64_t track_end;    ///< used for dts generation in fragmented movie files
 } MOVStreamContext;
 
 typedef struct MOVContext {

libavformat/mov.c

@@ -1639,6 +1639,7 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     st->nb_frames= total_sample_count;
     if (duration)
         st->duration= duration;
+    sc->track_end = duration;
     return 0;
 }
 
@@ -2233,7 +2234,7 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     if (flags & 0x001) data_offset        = avio_rb32(pb);
     if (flags & 0x004) first_sample_flags = avio_rb32(pb);
-    dts = st->duration - sc->time_offset;
+    dts    = sc->track_end - sc->time_offset;
     offset = frag->base_data_offset + data_offset;
     distance = 0;
     av_dlog(c->fc, "first sample flags 0x%x\n", first_sample_flags);
@@ -2263,7 +2264,7 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         sc->data_size += sample_size;
     }
     frag->moof_offset = offset;
-    st->duration = dts + sc->time_offset;
+    st->duration = sc->track_end = dts + sc->time_offset;
     return 0;
 }