[vdr] Re: bitstreamout-0.48pre3

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

On Mon, Oct 27, 2003 at 11:33:34PM +0100, Christian Tramnitz wrote:
> I connected ground but I used a plain (non-shielded) one-pin cable 
> (each)... like the ones used to connect the internal speaker.
> That was probably causing the distortions and I will try again with a 
> shielded cable.

Yep.  The problem is that the needed frequencies used for
the S/P-DIF transport protocol may cause distortions in the
video part if not shielded. Think about the sample frequency
with 48kHz for 16 bit stereo and for every 16 bit audio sample
a 32 bit transport word is used (bandwidth of 3MHz).  But due
to the fact of using biphased marked signal the upper bandwidth
is about 6MHz.

> 
> Btw, if you can only keep sound in sync with video, does bitstreamout 
> make sense at all? Is it also the same problem for AC3 output?
> If yes, AC3overDVB should be preferred over bitstreamout from my point 
> of view...

Two problems with AC3overDVB: Live isn't that what it could be,
and some receivers can not detect none audio data like AC3 because
there is no way to set the none audio status bit in the 32 bit transport
word.  Beside this you have problems with the bandwidth to the
DVB card because everey AC3 frame has to be included into
an 6144 byte large PCM frame (16bit stereo @ 48kHz) because every AC3
frame represents 32ms sound.


      Werner


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