[mythtv-users] MythTV channel buffer

Joe Votour joevph at yahoo.com
Sat Apr 15 01:24:27 UTC 2006



--- Greg Estabrooks <greg at phaze.org> wrote:

> > I agree that the current ring buffer
> implimentation is very very very poor.
> > On average it take 10-15 seconds for video to
> appear after starting live tv
> > and a good 5 seconds for it to change channels.
> Just for giggles I loaded
> 
> 
>  FYI this varies a LOT from user to user.  My LiveTV
> takes 2 seconds to start,
> and channel changes are 1.4 seconds. And yes I timed
> it. It use to take longer
> but after Isaac did his rewrite it. I never really
> use it, except for short 
> tests after hardware changes to make sure I haven't
> messed something up :)
> 
>  I don't know what it is that makes it so different
> from user to user but if 
> someone ever does track it down it will make a lot
> of people happy.
> 
>  And for the curious this is with PVR 250's, Nforce2
> board, xp2500+ and 
> 512Meg of ram. Timing from the remote frontend shows
> the same startup 
> time but channel changes are 1.8 seconds
> 
> 
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>
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> 

Not having looked at the code, I can only make
speculations, but there are some factors that I can
think of that would make a difference:
1. Combined frontend/backend versus seperate
frontend/backend - When I was running a seperate f/e
machines, I noticed that it took much longer (up to 15
seconds) to get LiveTV output.  This was back in
MythTV 0.17/0.18 though, I haven't tested this
configuration under 0.19 (though I will be soon).
2. The CPU speed of the backend and frontend - Faster
CPUs will definitely help.
3. PCI bus bandwidth/latency - Could it be that the
people who are seeing the delays have tons of tuners
and are recording tons of things at once?  Or have
they not tuned things with setpci?
4. (For seperate f/e setups) - Network latency. 
100/1000 Base-T, half/full-duplex, they make a
difference.

Those are just a few things that I can think of off
the top of my head.  My combined f/e machine works
quite is pretty guick on channel changes (no more than
3-4 seconds for ATSC, and faster for SD using a
PVR-x50 card).

-- Joe

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