[mythtv-users] mythmusic iec958 help

Mark Greenwood fatgerman at ntlworld.com
Sat Jul 5 15:46:45 UTC 2008


On Tuesday 01 July 2008 14:37:06 Steve Hodge wrote:
> On Tue, Jul 1, 2008 at 4:09 PM, Nick Rout <nick.rout at gmail.com> wrote:
> 
> > On Tue, Jul 1, 2008 at 3:04 PM, Alen Edwards
> > <allen.edwards at oldpaloalto.com> wrote:
> > > I don't think he wants alsa to do anything.   He has passthrough checked.
> > > alsa should not be doing anything except passing the data to the output.
> > > Something is telling alsa to process the data and the data rates then
> > become
> > > a problem.  At least, that is my understanding of it.
> >
> > Well passing a 44.1kHz stream through to a decoder that wants a 48kHz
> > stream is not going to work AFAIK.
> >
> 
> I doubt any modern decoder would fail to support both 48kHz and 44.1kHz,
> however I do know that some sound cards can only generate one rate or the
> other. That is why resampling via ALSA may be necessary.
> 
> Unless I am misunderstanding how "passthrough" works.
> >
> 
> Passthrough means "if this signal is AC3 or DTS, don't decode, just
> retransmit the original signal", but I believe the soundcard still needs to
> be able to send the signal at the right rate.

This may not be relevant, but I used to use a soundblaster Live under Windows (with Steinberg ASIO drivers). The Emu10k1 chip on which it is based can only run at 48KHz and will only output 48KHz via its spdif. (It will, however accept 44.1KHz input signals, I'm not sure how it manages that). In your case, it's very possible that ALSA is assuming that the chip requires 48KHz and will not send it anything else. In that case your only option may be to try simply switching passthrough off and allow some resampling to happen.

Mark

> 
> Cheers,
> Steve
> 




More information about the mythtv-users mailing list