au: set bit rate

libavformat/au.c

@@ -111,6 +111,7 @@ static int au_read_header(AVFormatContext *s)
     st->codec->codec_id = codec;
     st->codec->channels = channels;
     st->codec->sample_rate = rate;
+    st->codec->bit_rate    = channels * rate * bps;
     avpriv_set_pts_info(st, 64, 1, rate);
     return 0;
 }