avformat/mpegtsenc: warn users if codec isn't supported

The MPEG-TS muxer will mux streams with unsupported codec id
as a private data stream; this usually makes the stream
not recognizable by ffmpeg and likely other tools.

libavformat/mpegtsenc.c

@@ -382,6 +382,8 @@ static int mpegts_write_pmt(AVFormatContext *s, MpegTSService *service)
             stream_type = STREAM_TYPE_METADATA;
             break;
         default:
+            av_log(s, AV_LOG_WARNING, "Stream %d, codec %s, is muxed as a private data stream "
+                   "and may not be recognized upon reading.\n", i, avcodec_get_name(st->codecpar->codec_id));
             stream_type = STREAM_TYPE_PRIVATE_DATA;
             break;
         }