diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 84db468332..e7d604608d 100644
--- a/libavcodec/avcodec.h
+++ b/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.
      */