[vdr] Re: Softdevice + EPIA-M / Sound resampling

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

On Sun, Feb 01, 2004 at 10:44:50PM -0000, Colin Paton wrote:
> 
> > Audio<->DVB sync is much more critical.. _IF_ analog audio output is used,
> > you can simply adjust the playback frequency.. Like 47999Hz instead of
> > 48000Hz. Just calculate the audio timing error, and adjust the
> > frequency.. After a while, the frequency will settle to some value like
> > 47986Hz, and doesn't need big changes.
> 
> Will the ALSA drivers let you set this from user code, or does the
> resampling have to be done in software?
> 
> I'd like SPDIF to work too :-) I did read somewhere (I'm sure) that the AC97
> codec on that board works at 48kHz for all rates, therefore resampling must
> be done in software for 44.1kHz etc. I may be wrong however.

No, you're right here :^)  The S/P-DIF transport protocol use biphase marked
puls code ... you may vary for small differences the used clock (e.g. for
47986Hz this is 2*47986Hz if the hardware of the S/P-DIF out allows this) but
for 48->44.1kHz the data should be resampled.   The perfect solution would be
if the clock used for video could be used as input to generate the world clock
for audio out (slave mode).

          Werner


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