[vdr] [ANNOUNCE] bitstreamout plugin 0.80 (sound loop through sound card)

Dr. Werner Fink werner at suse.de
Wed Mar 16 13:52:12 CET 2005


On Wed, Mar 16, 2005 at 01:39:44PM +0100, Roland Praml wrote:
> > vdr-1.3.22 + bso-0.80 = Ok!
> > 
> > Slight A/V delay though. Will keep on tweeking tonight.
> 
> I've updated to 0.80, too. Now it works with newer recordings.
> 
> Just for my understanding:
> The A/V problem exists because the soundcard clock doesn't know
> anything about the DVB-clock respectively timestamp and there's
> no way to get the current video-timestamp which is displayed at
> the moment. So the only way in my eyes is to use the spdif of
> the DVB-card for perfect A/V-sync.
> 
> There are different ways to transfer AC3 over spdif:
> - a real AC3 stream (like DVD playes do)
> - AC3 embedded in PCM (like AC3overDVB and bso)

There are two methods:  a 32bit method which is a transport
layer similar to S/P-DIF but only for AC3 (you need HW
access to the S/P-DIF interface of the soundcard) and
the other method is 16bit using a nonlinear PCM stream
accordingly to ISO/IEC61937.  The later one requrires
in the 32bit S/P-DIF transport layer the non-audio status bit.
Nevertheless many AV receivers do detected _and_ handle
the nonlinear PCM stream within the S/P-DIF transport layer

-> http://www.epanorama.net/documents/audio/spdif.html


> 
> bso can set the nonaudio-bit, AC3overDVB can't.
> 
> Why? is this a hardware limitation? Can it theoretically 
> worked around by some soldering etc?

Ask TI, I don't know.

> 
> Long time ago there were so called 'copy-bit killer'
> Can I set the nonaudio with a similar circuit.

Depends if this circuit works on the payload of the 32bit
S/P-DIF transport layer or on the status bits of the transport
layer its self ... the later one should be done.

> As other mentioned this should also be done by a soundcard
> by reading from spdif-in, set the bit, and writing to spdif-out
> 
> (it's definitely a bug in the sony-firmware why my receiver
> can't play AC3 over DVB. I've a AC3 and DTS CD, the surround
> sound is wrapped in PCM-frames. DTS is played fine, AC3 not.
> The behaviour is the same as if replaying AC3 over DVB.
> BUT if I skip quickly from an DTS to an AC3 track the receiver
> sometimes "hangs" on DTS but plays AC3 WITH SOUND)

I don't think its a bug ... it is not specified to play
16 bit nonlinear PCM without marking the 32bit S/P-DIF
transport layer as nonlinear.  For all the others which
can handle this ... it's a nice feature.


        Werner

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