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

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> On Tue, Feb 10, 2009 at 11:39:24AM +0530, Jai Menon wrote:
>> 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.
>
> looks ok assuming mans has no sugestions for improvment

No immediate ideas here.  The entire stream type detection code could
use a cleanup, but that's not Jai's job.

-- 
M?ns Rullg?rd
mans at mansr.com