avformat/matroskaenc: Don't pretend to be able to mux RV30

The demuxer uses a extradata offset of 26, so we would need
to recreate the missing 26 bytes somehow in the muxer, but
we just don't. Remuxed files (like real/rv30.rm from the FATE-suite)
don't work due to missing extradata.

(The extradata offset also applies to RV40 and the extradata
is indeed lost upon remuxing, yet remuxing real/spygames-2MB.rmvb
works; our RV40 decoder does not use extradata at all.)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/matroskaenc.c

@@ -3300,7 +3300,8 @@ static int mkv_init(struct AVFormatContext *s)
             s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RA_288 ||
             s->streams[i]->codecpar->codec_id == AV_CODEC_ID_SIPR ||
             s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RV10 ||
-            s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RV20) {
+            s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RV20 ||
+            s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RV30) {
             av_log(s, AV_LOG_ERROR,
                    "The Matroska muxer does not yet support muxing %s\n",
                    avcodec_get_name(s->streams[i]->codecpar->codec_id));
@@ -3430,11 +3431,6 @@ static const AVCodecTag additional_audio_tags[] = {
     { AV_CODEC_ID_NONE,      0xFFFFFFFF }
 };
 
-static const AVCodecTag additional_video_tags[] = {
-    { AV_CODEC_ID_RV30,      0xFFFFFFFF },
-    { AV_CODEC_ID_NONE,      0xFFFFFFFF }
-};
-
 static const AVCodecTag additional_subtitle_tags[] = {
     { AV_CODEC_ID_DVB_SUBTITLE,      0xFFFFFFFF },
     { AV_CODEC_ID_DVD_SUBTITLE,      0xFFFFFFFF },
@@ -3506,7 +3502,7 @@ const FFOutputFormat ff_matroska_muxer = {
                          AVFMT_TS_NONSTRICT | AVFMT_ALLOW_FLUSH,
     .p.codec_tag       = (const AVCodecTag* const []){
          ff_codec_bmp_tags, ff_codec_wav_tags,
-         additional_audio_tags, additional_video_tags, additional_subtitle_tags, 0
+         additional_audio_tags, additional_subtitle_tags, 0
     },
     .p.subtitle_codec  = AV_CODEC_ID_ASS,
     .query_codec       = mkv_query_codec,