add AVRn fourcc

Originally committed as revision 8572 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/riff.c

@@ -104,6 +104,7 @@ const AVCodecTag codec_bmp_tags[] = {
     { CODEC_ID_MJPEG, MKTAG('M', 'J', 'L', 'S') }, /* JPEG-LS custom FOURCC for avi - decoder */
     { CODEC_ID_MJPEG, MKTAG('j', 'p', 'e', 'g') },
     { CODEC_ID_MJPEG, MKTAG('I', 'J', 'P', 'G') },
+    { CODEC_ID_MJPEG, MKTAG('A', 'V', 'R', 'n') },
     { CODEC_ID_JPEGLS, MKTAG('M', 'J', 'L', 'S') }, /* JPEG-LS custom FOURCC for avi - encoder */
     { CODEC_ID_HUFFYUV, MKTAG('H', 'F', 'Y', 'U') },
     { CODEC_ID_FFVHUFF, MKTAG('F', 'F', 'V', 'H') },