[vdr] Re: AC3 over DVB-s is possible - Part2

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

On Tue, Feb 19, 2002 at 11:13:28AM +0100, Wolfgang Fiesel wrote:
> Hello,
> 
> as I promised last week,
> now AC-3 over Digital Output (SPDIF) for DVB-S is reality (recordings
> and DVD playback).
> Of course if the recordings doesn't include any AC-3 data the SDPIF
> output will be operate like before (raw PCM).
> I'm using DVB-S version 2.1 (Hauppage)

Fine ... the only question I've: Why the DVB developers have
said that this wouldn't work.  This because I've supposed this
a half year ago at the linux-dvb@linuxtv.org list.

> It's time to throw away the soundcard and forget the -a switch.
> Nevertheless I modified the code very carefully and minimized the
> patch effort. Therefore all previous AC-3 playmodes (-a switch) should
> also operate like before.
> 
> How does it work ?
> The secret is the IEC 61937 paper which describes the wrapping of AC-3,
> MP3, DTS, ... into raw 16 bit PCM data. Finally the LPCM
> transport feature of the DVB driver was the key to realise it.

This is exactly how ac3dec with -C/-P and ac3play it do.

> 
> The patch is related to Klaus latest update version (vdr-0.99) to get a
> chance
> to be integrated if the test phase should be successfully. Since two
> days I've check it by myself with different AC3 recordings and DVD's. Up

Hmmm ... please have a look on send_ipack() in driver/dvb_filter.c
of the DVB driver 0.9.4.   Maybe it is possible to do the same
IEC 61937 stuff directly in the DVB driver.  For replay AND
normal TV viewing.  AFAIS in send_ipack() the mpeg stream will be
scanned if p->repack_subids is true (by default it is set to
false at init_ipack()).   Maybe the wrapping of AC-3 into raw 16 bit
linear PCM could be done at send_ipack() and the resulting PCM
stream forwarded to SDPIF output as a replacement of the MPEG
decoded PCM stream.


       Werner