Ensure that muxer and encoder aspect ratios match. So no

invalid files are generated.

Originally committed as revision 15367 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -2457,6 +2457,10 @@ int av_write_header(AVFormatContext *s)
                 av_log(s, AV_LOG_ERROR, "dimensions not set\n");
                 return -1;
             }
+            if(av_cmp_q(st->sample_aspect_ratio, st->codec->sample_aspect_ratio)){
+                av_log(s, AV_LOG_ERROR, "Aspect ratio mismatch between encoder and muxer layer\n");
+                return -1;
+            }
             break;
         }