recommit of

slightly cleaner width / height comment

Originally committed as revision 2353 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -482,7 +482,7 @@ typedef struct AVCodecContext {
     /**
      * width / height.
      * - encoding: MUST be set by user. 
-     * - decoding: set by user, some codecs might override / change it during playback
+     * - decoding: set by user if known, codec should override / dynamically change if needed
      */
     int width, height;