extradata endianness comment

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@4674 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/avcodec.h

@@ -738,6 +738,7 @@ typedef struct AVCodecContext {
      * mpeg4: global headers (they can be in the bitstream or here)
      * the allocated memory should be FF_INPUT_BUFFER_PADDING_SIZE bytes larger
      * then extradata_size to avoid prolems if its read with the bitstream reader
+     * the bytewise contents of extradata must not depend on the architecture or cpu endianness
      * - encoding: set/allocated/freed by lavc.
      * - decoding: set/allocated/freed by user.
      */