Added M701 codec_tag for mpeg2video

Originally committed as revision 23513 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/riff.c

@@ -123,6 +123,7 @@ const AVCodecTag ff_codec_bmp_tags[] = {
     { CODEC_ID_MPEG2VIDEO,   MKTAG('L', 'M', 'P', '2') }, /* Lead MPEG2 in avi */
     { CODEC_ID_MPEG2VIDEO,   MKTAG('s', 'l', 'i', 'f') },
     { CODEC_ID_MPEG2VIDEO,   MKTAG('E', 'M', '2', 'V') },
+    { CODEC_ID_MPEG2VIDEO,   MKTAG('M', '7', '0', '1') }, /* Matrox MPEG2 intra-only */
     { CODEC_ID_MJPEG,        MKTAG('M', 'J', 'P', 'G') },
     { CODEC_ID_MJPEG,        MKTAG('L', 'J', 'P', 'G') },
     { CODEC_ID_MJPEG,        MKTAG('d', 'm', 'b', '1') },