mkv: support vp9 tag

libavcodec/avcodec.h

@@ -267,6 +267,7 @@ enum AVCodecID {
     AV_CODEC_ID_MTS2,
     AV_CODEC_ID_CLLC,
     AV_CODEC_ID_MSS2,
+    AV_CODEC_ID_VP9,
 
     /* various PCM "codecs" */
     AV_CODEC_ID_FIRST_AUDIO = 0x10000,     ///< A dummy id pointing at the start of audio codecs

libavformat/matroska.c

@@ -79,6 +79,7 @@ const CodecTags ff_mkv_codec_tags[]={
     {"V_THEORA"         , AV_CODEC_ID_THEORA},
     {"V_UNCOMPRESSED"   , AV_CODEC_ID_RAWVIDEO},
     {"V_VP8"            , AV_CODEC_ID_VP8},
+    {"V_VP9"            , AV_CODEC_ID_VP9},
 
     {""                 , AV_CODEC_ID_NONE}
 };