lavf: print a matching tag in case of code tag validation failure

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

libavformat/utils.c

@@ -3179,11 +3179,12 @@ int avformat_write_header(AVFormatContext *s, AVDictionary **options)
             }
             if(st->codec->codec_tag){
                 if (!validate_codec_tag(s, st)) {
-                    char tagbuf[32];
+                    char tagbuf[32], cortag[32];
                     av_get_codec_tag_string(tagbuf, sizeof(tagbuf), st->codec->codec_tag);
+                    av_get_codec_tag_string(cortag, sizeof(cortag), av_codec_get_tag(s->oformat->codec_tag, st->codec->codec_id));
                     av_log(s, AV_LOG_ERROR,
-                           "Tag %s/0x%08x incompatible with output codec id '%d'\n",
-                           tagbuf, st->codec->codec_tag, st->codec->codec_id);
+                           "Tag %s/0x%08x incompatible with output codec id '%d' (%s)\n",
+                           tagbuf, st->codec->codec_tag, st->codec->codec_id, cortag);
                     ret = AVERROR_INVALIDDATA;
                     goto fail;
                 }