[FFmpeg-devel] [PATCH] dvd audio sub-stream handling in the mpeg2 demuxer

[Michael Niedermayer]

On Mon, Feb 09, 2009 at 10:02:51AM +0530, Jai Menon wrote:
> Hi,
> 
> Attached patch allows for demuxing of audio substreams stored as 0x06 type.
> Raw a/52 and subtitle detection is not included because of lack of a sample.
> Fixes issue 725 : MPEG2 PS with PCM audio
> 
> -- 
> Regards,
> 
> Jai

> Index: libavformat/mpeg.c
> ===================================================================
> --- libavformat/mpeg.c	(revision 16998)
> +++ libavformat/mpeg.c	(working copy)
> @@ -450,6 +450,23 @@
>          } else if(es_type == STREAM_TYPE_AUDIO_AC3){
>              codec_id = CODEC_ID_AC3;
>              type = CODEC_TYPE_AUDIO;
> +        } else if(es_type == STREAM_TYPE_PRIVATE_DATA){
> +            uint8_t audio_id;
> +
> +            // probe for dvd audio sub-stream
> +            type = CODEC_TYPE_AUDIO;
> +            audio_id = get_byte(s->pb);
> +            url_fseek(s->pb, -1, SEEK_CUR);
> +            switch(audio_id & 0xe0) {
> +                case 0xa0:  codec_id = CODEC_ID_PCM_DVD;
> +                            break;
> +                case 0x80:  if((audio_id & 0xf8) == 0x88)
> +                                 codec_id = CODEC_ID_DTS;
> +                            else codec_id = CODEC_ID_AC3;
> +                            break;
> +                default:    av_log(s, AV_LOG_ERROR, "Unknown 0x1bd sub-stream\n");
> +                            goto skip;
> +            }
>          } else {
>              goto skip;
>          }
> @@ -508,7 +525,17 @@
>   found:
>      if(st->discard >= AVDISCARD_ALL)
>          goto skip;
> -    if (startcode >= 0xa0 && startcode <= 0xaf) {
> +
> +    if(startcode == 0x1bd) {
> +        // skip dvd audio sub-stream header
> +        url_fskip(s->pb, 4);
> +        len -= 4;
> +    }
> +
> +    if ((startcode >= 0xa0 && startcode <= 0xaf) ||
> +        ((startcode == 0x1bd) &&
> +        ((st->codec->codec_id == CODEC_ID_PCM_S16BE) ||
> +         (st->codec->codec_id == CODEC_ID_PCM_DVD)))) {
>          int b1, freq;
>  
>          /* for LPCM, we just skip the header and consider it is raw

what about:
     }
 
     es_type = m->psm_es_type[startcode & 0xff];
-    if(es_type > 0){
+    if(es_type > 0 && es_type != STREAM_TYPE_PRIVATE_DATA){
         if(es_type == STREAM_TYPE_VIDEO_MPEG1){
             codec_id = CODEC_ID_MPEG2VIDEO;
             type = CODEC_TYPE_VIDEO;
...

and then have the detection under if(startcode == 0x1bd)
this seems more robust but maybe iam missing something?

also id read the 4 byte header before
 /* now find stream */
    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];
        if (st->id == startcode)
            goto found;
    }
that would avoid the seek back and "skip dvd audio sub-stream header"

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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