diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 623da5e166..a5fd2e7386 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -3832,6 +3832,10 @@ int avcodec_open2(AVCodecContext *avctx, AVCodec *codec, AVDictionary **options)
  * samples should be 16 byte aligned unless the CPU doesn't need it
  * (AltiVec and SSE do).
  *
+ * @note Codecs which have the CODEC_CAP_DELAY capability set have a delay
+ * between input and output, these need to be fed with avpkt->data=NULL,
+ * avpkt->size=0 at the end to return the remaining frames.
+ *
  * @param avctx the codec context
  * @param[out] samples the output buffer, sample type in avctx->sample_fmt
  * @param[in,out] frame_size_ptr the output buffer size in bytes