output a pcr as soon as possible, patch by Mike Scheutzow, scheutzow at alcatel-lucent dot com

Originally committed as revision 21197 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mpegtsenc.c

@@ -485,6 +485,9 @@ static int mpegts_write_header(AVFormatContext *s)
     else
         ts->mux_rate = total_bit_rate;
 
+    // output a PCR as soon as possible
+    service->pcr_packet_count = service->pcr_packet_period;
+
     // adjust pcr
     ts->cur_pcr /= ts->mux_rate;