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

[Jai Menon]

On Tue, Feb 10, 2009 at 6:23 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> 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?

yes thats better, i was just trying hard not to change the structure
of the existing code.

> 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"

reworked and revised patch attached.

[...]


-- 
Regards,

Jai
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