riff: add VP9 fourcc

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/riff.c

@@ -256,6 +256,7 @@ const AVCodecTag ff_codec_bmp_tags[] = {
     { AV_CODEC_ID_VP6F,         MKTAG('V', 'P', '6', 'F') },
     { AV_CODEC_ID_VP6F,         MKTAG('F', 'L', 'V', '4') },
     { AV_CODEC_ID_VP8,          MKTAG('V', 'P', '8', '0') },
+    { AV_CODEC_ID_VP9,          MKTAG('V', 'P', '9', '0') },
     { AV_CODEC_ID_ASV1,         MKTAG('A', 'S', 'V', '1') },
     { AV_CODEC_ID_ASV2,         MKTAG('A', 'S', 'V', '2') },
     { AV_CODEC_ID_VCR1,         MKTAG('V', 'C', 'R', '1') },