lavf: fill in past dts based on reordered pts once the delay becomes known.

Previously we had ignored the past dts and just filled in from the
point where we have had sufficient information.

This should fix Ticket1734
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -940,15 +940,21 @@ static void update_initial_timestamps(AVFormatContext *s, int stream_index,
 {
     AVStream *st= s->streams[stream_index];
     AVPacketList *pktl= s->parse_queue ? s->parse_queue : s->packet_buffer;
+    int64_t pts_buffer[MAX_REORDER_DELAY];
     int64_t shift;
+    int i, delay;
 
     if(st->first_dts != AV_NOPTS_VALUE || dts == AV_NOPTS_VALUE || st->cur_dts == AV_NOPTS_VALUE || is_relative(dts))
         return;
 
+    delay = st->codec->has_b_frames;
     st->first_dts= dts - (st->cur_dts - RELATIVE_TS_BASE);
     st->cur_dts= dts;
     shift = st->first_dts - RELATIVE_TS_BASE;
 
+    for (i=0; i<MAX_REORDER_DELAY; i++)
+        pts_buffer[i] = AV_NOPTS_VALUE;
+
     if (is_relative(pts))
         pts += shift;
 
@@ -963,6 +969,14 @@ static void update_initial_timestamps(AVFormatContext *s, int stream_index,
 
         if(st->start_time == AV_NOPTS_VALUE && pktl->pkt.pts != AV_NOPTS_VALUE)
             st->start_time= pktl->pkt.pts;
+
+        if(pktl->pkt.pts != AV_NOPTS_VALUE && delay <= MAX_REORDER_DELAY && has_decode_delay_been_guessed(st)){
+            pts_buffer[0]= pktl->pkt.pts;
+            for(i=0; i<delay && pts_buffer[i] > pts_buffer[i+1]; i++)
+                FFSWAP(int64_t, pts_buffer[i], pts_buffer[i+1]);
+            if(pktl->pkt.dts == AV_NOPTS_VALUE)
+                pktl->pkt.dts= pts_buffer[0];
+        }
     }
     if (st->start_time == AV_NOPTS_VALUE)
         st->start_time = pts;