Init SCR in mpeg muxer based on first DTS.

This fixes issues if the first DTS is far away from 0.

Originally committed as revision 25383 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mpegenc.c

@@ -1160,6 +1160,8 @@ static int mpeg_mux_write_packet(AVFormatContext *ctx, AVPacket *pkt)
 
     pts= pkt->pts;
     dts= pkt->dts;
+    if(!s->last_scr)
+        s->last_scr= dts;
 
     if(pts != AV_NOPTS_VALUE) pts += preload;
     if(dts != AV_NOPTS_VALUE) dts += preload;

tests/ref/lavf/mpg

@@ -1,3 +1,3 @@
-e36a005ecca9add8bda6e0655d03716f *./tests/data/lavf/lavf.mpg
+eed66277633e53724e58e3fca2709f41 *./tests/data/lavf/lavf.mpg
 372736 ./tests/data/lavf/lavf.mpg
 ./tests/data/lavf/lavf.mpg CRC=0x2b39ed74