Make the error message issued in case of invalid codec tag more

informative.

Originally committed as revision 23423 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -2656,9 +2656,11 @@ int av_write_header(AVFormatContext *s)
         if(s->oformat->codec_tag){
             if(st->codec->codec_tag){
                 if (!validate_codec_tag(s, st)) {
+                    char tagbuf[32];
+                    av_get_codec_tag_string(tagbuf, sizeof(tagbuf), st->codec->codec_tag);
                     av_log(s, AV_LOG_ERROR,
-                           "Tag 0x%08x incompatible with output codec\n",
-                           st->codec->codec_tag);
+                           "Tag %s/0x%08x incompatible with output codec '%s'\n",
+                           tagbuf, st->codec->codec_tag, st->codec->codec->name);
                     return AVERROR_INVALIDDATA;
                 }
             }else