[vdr] DVD with AC3 audio question

Kartsa kari at kniivila.com
Tue Mar 7 08:04:59 CET 2006

> [mailto:vdr-bounces at linuxtv.org] On Behalf Of Dr. Werner Fink
> > 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

Now I tried without the -a option and got the PCM light on in the receiver
but there were no sound. Not even noise. I got VDR somehow freesed while I
was testing when I was trying to select the audio (for some reason there
seemed to be two audio tracks on the DVD even though I had put there only
one :/). There was something like "tried to open OSD although OSD allready
open" in the log file (I can not verify that right now). So I had to reboot
in order to get normal working state again. Then it began to record and I
could not test with a commercial DVD (wife factor, you know). But I have to
say that the DVD I made works fine in my set top DVD player.

Anyway the reason can then be my receiver if it tests the bit and ignores
PCM structure but somehow stops the noise.

So how is it that this setting seems to work for some and not for some
(unles it is all about the receiver).

I will test with another DVD still and report what happens :)


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