two more typos spotted by Mike

Originally committed as revision 12524 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3enc.c

@@ -676,7 +676,7 @@ static int AC3_encode_init(AVCodecContext *avctx)
     } else {
         /* use default bandwidth setting */
         /* XXX: should compute the bandwidth according to the frame
-           size, so that we avoid anoying high freq artifacts */
+           size, so that we avoid annoying high frequency artifacts */
         bw_code = 50;
     }
     for(ch=0;ch<s->nb_channels;ch++) {