Merge commit '7a5f4f6853047eea74a6443d73f4d74d52b2799f'

* commit '7a5f4f6853047eea74a6443d73f4d74d52b2799f':
  lavf: extend avg_frame_rate documentation.

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

libavformat/avformat.h

@@ -835,6 +835,10 @@ typedef struct AVStream {
 
     /**
      * Average framerate
+     *
+     * - demuxing: May be set by libavformat when creating the stream or in
+     *             avformat_find_stream_info().
+     * - muxing: May be set by the caller before avformat_write_header().
      */
     AVRational avg_frame_rate;