avcodec: Resolve the codec_id compatibility issue.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avcodec.h

@@ -47,7 +47,8 @@
  *
  * If you add a codec ID to this list, add it so that
  * 1. no value of a existing codec ID changes (that would break ABI),
- * 2. it is as close as possible to similar codecs.
+ * 2. Give it a value which when taken as ASCII is recognized uniquely by a human as this specific codec.
+ *    This ensures that 2 forks can independantly add CodecIDs without producing conflicts.
  */
 enum CodecID {
     CODEC_ID_NONE,