[vdr] DVD with AC3 audio question

Dr. Werner Fink werner at suse.de
Mon Mar 6 15:20:34 CET 2006

On Sun, Mar 05, 2006 at 02:42:03PM +0100, Peter Juszack wrote:
> You said that you never used AC3 before because you do not receive 
> AC3-channels from your cable network. On my Hauppauge FF-card the 
> firmware must do a trick do deliver AC3 on the SPDIF by encapsulating 
> the AC3 pakets in PCM. Some AV-receivers cannot handle that. I believe 
> that Technotrend is the same.

For S/P-DIF the AC3 pakets are encapsluated into non-linear PCM[2].
The problem is that within the S/P-DIF containers[1] for the AC3 data
there are some more bits which are used to indicate `AC3 used'.
Now the hardware of the DVB-S cards can not set this `AC3 used'
bit and if AV receivers test for this bit and ignore the special
PCM structure[2] the AC3 data will be handled as linear PCM which
is generating nasty noise.

[1] S/P-DIF is part of ISO/IEC 60958
[2] Nonlinear PCM for AC3 over S/P-DIF as described in ISO/IEC 61937


AC3 loop through sound card http://bitstreamout.sourceforge.net/
Howto http://www.vdr-portal.de/board/thread.php?threadid=1958
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