Fix pts->dts conversion init for non-zero initial value for pts.

Patch by Daniel Kristjansson, danielk cuymedia net

Originally committed as revision 22297 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -2695,7 +2695,7 @@ static int compute_pkt_fields2(AVFormatContext *s, AVStream *st, AVPacket *pkt){
     if(pkt->pts != AV_NOPTS_VALUE && pkt->dts == AV_NOPTS_VALUE && delay <= MAX_REORDER_DELAY){
         st->pts_buffer[0]= pkt->pts;
         for(i=1; i<delay+1 && st->pts_buffer[i] == AV_NOPTS_VALUE; i++)
-            st->pts_buffer[i]= (i-delay-1) * pkt->duration;
+            st->pts_buffer[i]= pkt->pts + (i-delay-1) * pkt->duration;
         for(i=0; i<delay && st->pts_buffer[i] > st->pts_buffer[i+1]; i++)
             FFSWAP(int64_t, st->pts_buffer[i], st->pts_buffer[i+1]);