avformat/cafenc: disable muxing Opus streams

We're not writing a kuki chunk because its contents for Opus are currently
unknown, so it's best if we don't allow the creation of non spec compliant
files.

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/cafenc.c

@@ -121,6 +121,7 @@ static int caf_write_init(struct AVFormatContext *s)
 
     switch (par->codec_id) {
     case AV_CODEC_ID_AAC:
+    case AV_CODEC_ID_OPUS:
         av_log(s, AV_LOG_ERROR, "muxing codec currently unsupported\n");
         return AVERROR_PATCHWELCOME;
     }