[vdr] Re: [linux-dvb] Dolby Digital through DVB - How?

["Dr. Werner Fink" <werner@suse.de>]

On Thu, Aug 28, 2003 at 08:44:49PM +0200, Robert Schlabbach wrote:
> From: "Dr. Werner Fink" <werner@suse.de>
> > > PID 257: ITU-T Rec. H.222.0 | ISO/IEC 13818-1 PES packets containing
> > > private data
> > > unknown descriptor 0x6A: 00
> > > Stream Identifier: 17
> >
> > This one ... but please note that this Private Stream 1 does _not_
> > use a valid sub stream with 0x80 as mark for a DD stream but
> > simply puts each DD frame into the payload of the PS1
> > (remark: on some channels more DD frames are included in several
> >  PS1 packets with overlapping DD frames, but the PS1 packet with
> >  the Copyright bit set starts always with a DD frame).
> >
> > AFIAK the DVB channesl do not use sub stream magic.
> 
> Thanks for the clarification! So I can assume that the substream which MTV
> broadcasts cannot be a valid DD/AC-3 stream and that no DVB receivers on
> the market would recognize it as such? In that case, the fix for the
> software would simply be to not recognize 0x81 substreams as AC-3 audio...

You may record a minute or so with VDR, than use the mpegtools
to extract the PS1 stream from the multiplexed PES stream
(use 0xBD as ID for extract_pes for example).  Then have a look
into the stream with

       od -v -t x1 ps1.mpg | less

You'll see the PS1 start header 0x00 0x00 0x01 0xBD followed by
two bytes giving the package length, some more bytes declaring
the availability of e.g. PTS (Present Time Stamp), copyright aligment,
... which may used in the header ... after this header info the payload
follows ...  for AC3 two methods are know ... the DVD method with an own
sub stream using its own header (4 bytes with the magic start byte 0x80
... 0x87, for 7 AC3 streams, followed by one byte giving the number of
AC3 frames two bytes declaring the offset to the next AC3 frame start)
... and the brutal DVB method for Pro7 and Premiere ... or maybe there
is a third method, the method of MTV ;^)


        Werner


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