avformat/matroskaenc: Allow VP9 and Opus in webm

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

libavformat/matroskaenc.c

@@ -619,9 +619,11 @@ static int mkv_write_tracks(AVFormatContext *s)
         }
 
         if (mkv->mode == MODE_WEBM && !(codec->codec_id == AV_CODEC_ID_VP8 ||
+                                        codec->codec_id == AV_CODEC_ID_VP9 ||
+                                      ((codec->codec_id == AV_CODEC_ID_OPUS)&&(codec->strict_std_compliance <= FF_COMPLIANCE_EXPERIMENTAL)) ||
                                         codec->codec_id == AV_CODEC_ID_VORBIS)) {
             av_log(s, AV_LOG_ERROR,
-                   "Only VP8 video and Vorbis audio are supported for WebM.\n");
+                   "Only VP8,VP9 video and Vorbis,Opus(experimental, use -strict -2) audio are supported for WebM.\n");
             return AVERROR(EINVAL);
         }