lavc doxy: document that avcodec_flush_buffers() invalidates decoded frames

libavcodec/avcodec.h

@@ -3388,8 +3388,8 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
  *                   to the frame if av_frame_is_writable() returns 1.
  *                   When AVCodecContext.refcounted_frames is set to 0, the returned
  *                   reference belongs to the decoder and is valid only until the
- *                   next call to this function or until closing the decoder.
- *                   The caller may not write to it.
+ *                   next call to this function or until closing or flushing the
+ *                   decoder. The caller may not write to it.
  * @param[out] got_frame_ptr Zero if no frame could be decoded, otherwise it is
  *                           non-zero.
  * @param[in]  avpkt The input AVPacket containing the input buffer.
@@ -3437,8 +3437,8 @@ int avcodec_decode_audio4(AVCodecContext *avctx, AVFrame *frame,
  *             to the frame if av_frame_is_writable() returns 1.
  *             When AVCodecContext.refcounted_frames is set to 0, the returned
  *             reference belongs to the decoder and is valid only until the
- *             next call to this function or until closing the decoder. The
- *             caller may not write to it.
+ *             next call to this function or until closing or flushing the
+ *             decoder. The caller may not write to it.
  *
  * @param[in] avpkt The input AVpacket containing the input buffer.
  *            You can create such packet with av_init_packet() and by then setting
@@ -4060,7 +4060,13 @@ int avcodec_fill_audio_frame(AVFrame *frame, int nb_channels,
                              int buf_size, int align);
 
 /**
- * Flush buffers, should be called when seeking or when switching to a different stream.
+ * Reset the internal decoder state / flush internal buffers. Should be called
+ * e.g. when seeking or when switching to a different stream.
+ *
+ * @note when refcounted frames are not used (i.e. avctx->refcounted_frames is 0),
+ * this invalidates the frames previously returned from the decoder. When
+ * refcounted frames are used, the decoder just releases any references it might
+ * keep internally, but the caller's reference remains valid.
  */
 void avcodec_flush_buffers(AVCodecContext *avctx);