[mythtv] LiveTV playback timing problems

Paul Sykes pdsykes at gmail.com
Sat Nov 27 13:41:14 UTC 2004


On Sat, 27 Nov 2004 10:07:26 +0000, Ed Wildgoose <lists at wildgooses.com> wrote:
>  And was that the problem? Just find out for goodness sake?! I am entirely
> new to linux and I do not know how to change the sample rate of my sound
> card. I was hoping that somebody would tell me through this list 
>  You don't (and usually can't) set the sample rate of your soundcard.  The
> programmer requests the rate that they want and the card usually gives it to
> them.  Sometimes if you have a digital receiver, then the output gets stuck
> at 48Khz because that's all the card designers felt like implementing for
> spdif.  Ocassionally (much more rare I think), the card gets locked in the
> same way at 44Khz.
>  Suprisingly, from the angle I am sitting here I can't quite see which sound
> card you even have....
Ok, I have managed to use /proc/asound to show that the soundcard is
receiving and playing a 48khz signal so I do not think it is related
to that.

My soundcard, as I said in my last e-mail, is a C-Meida CMI 8738 PCI
(onboard) soundacard.  I have also tried a usb sp/dif soundcard that I
have and exactly the same thing happens.

I do not think that this is a problem related to sound/video hardware,
I think that it is something to do with the linux timing services,
like the RTC.
>  I am using an LCD monitor and the refresh rate is set to 75hz, it is also
> connect via DVI rather than a standard VGA connector. Could this be a
> problem. 
>  It could be.  Try changing the refresh rate to 50Hz.  You will probably
> need to generate a new modeline (there is some X app that I forget the name
> of which does it automatically).

I have now tried this and the problem still persists.

>  Try also checking your myth options in the tv playback settings menu. 
> Stuff like "use video as timebase" is not going to work here.
>  Sounds wierd.  You really do need to try to provide more info to get this
> debugged though

The reason why I approached this list was to get some help, I have
given you all of the information that you have asked for and I am not
entirely sure what else might be helpful.  I have given you a complete
list of my hardware, the version of myth I have installed, and I have
now tried every version from 0.15-r1 to the current cvs.

Still I have had no answer as to what MythTV uses as it's timer
source, is there a developer out there who could tell me?  Is the
source different for the video/sound and the video position timer?
>  Good luck
>  Ed W

Thanks for your help so far.


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