correctly compute bit rate for compressed audio, should fix seeking in aiff

Originally committed as revision 12327 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/aiff.c

@@ -152,7 +152,8 @@ static unsigned int get_aiff_header(ByteIOContext *pb, AVCodecContext *codec,
     if (!codec->block_align)
         codec->block_align = (codec->bits_per_sample * codec->channels) >> 3;
 
-    codec->bit_rate = codec->sample_rate * (codec->block_align << 3);
+    codec->bit_rate = (codec->frame_size ? codec->sample_rate/codec->frame_size :
+                       codec->sample_rate) * (codec->block_align << 3);
 
     /* Chunk is over */
     if (size)