Clarify timestamps related error messages in compute_pkt_fields2().

Originally committed as revision 26308 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -2917,12 +2917,12 @@ static int compute_pkt_fields2(AVFormatContext *s, AVStream *st, AVPacket *pkt){
 
     if(st->cur_dts && st->cur_dts != AV_NOPTS_VALUE && st->cur_dts >= pkt->dts){
         av_log(s, AV_LOG_ERROR,
-               "st:%d error, non monotone timestamps %"PRId64" >= %"PRId64"\n",
+               "Application provided invalid, non monotonically increasing dts to muxer in stream %d: %"PRId64" >= %"PRId64"\n",
                st->index, st->cur_dts, pkt->dts);
         return -1;
     }
     if(pkt->dts != AV_NOPTS_VALUE && pkt->pts != AV_NOPTS_VALUE && pkt->pts < pkt->dts){
-        av_log(s, AV_LOG_ERROR, "st:%d error, pts < dts\n", st->index);
+        av_log(s, AV_LOG_ERROR, "pts < dts in stream %d\n", st->index);
         return -1;
     }