[linux-dvb] AC3 via S-PDIF

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Maybe somebody with deeper knowledge about this can help me out here:

I understand that an AC3 decoder accepts the digital data through
either a coaxial or optical input line. That line (or the protocol?)
is specified as "S-PDIF". This is a unidirectional link and there
is no handshake.

Since the hardware on the DVB-S card apparently can't be used to
send the AC3 data stream to an external AC3 decoder (at least that's
what the driver developers wrote here on the list, IIRC), and I don't
want to install a sound card in my VDR box just because of the S-PDIF
interface (it's not because of the costs, it's because such a card
would occupy one of my valuable PCI slots ;-) I was wondering what
is actually necessary to implement an S-PDIF interface. The electrical
circuitry appears to be pretty trivial (see for instance "elektor" 7/8 2000,
page 37). And the actual data I guess would consist mainly of the AC3
data stream as received from the transponder. The question now is: does
that data have to be modified in any way (like adding a ninth bit, repackaging
or stunts like that), or is it just to be sent "as is"?

What I am thinking of would be a small electrical interface connected
to the serial or parallel interface. The data could then just be sent to 
the respective device and we would not need any special sound card driver
(and we would also not have to install a sound card :-)

Is this idea in any way feasible - or am I missing something important
here? Would the bandwidth of the serial or parallel interface be enough
for the AC3 data stream?

I do admit that my knowledge of S-PDIF is next to zero - but I hope
to change that...

Klaus
-- 
_______________________________________________________________

Klaus Schmidinger                       Phone: +49-8635-6989-10
CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
Hofmark 2                               Email:   kls@cadsoft.de
D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
_______________________________________________________________


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