[mythtv-users] Smoothing out the channel change script

Viitasaari public at viitasaari.ca
Fri Nov 17 05:35:07 UTC 2006


So this is a fact of life with MythTV?

Q: When using live TV, why is there a delay between the moment I change
the channel and the time the channel actually changes?
When you are watching live tv in Myth, you are actually watching content
which has first been written as a file to the hard disk. In doing so,
the 'live TV' that you are watching is actually TV that has been
captured a few seconds beforehand. Whenever you change channel, the old
file has to be removed and a new file created. The fact that this takes
a couple of seconds is responsible for the gap you are seeing in between
channel changes.

Although this doesn't sound too good, it is necessary to create this
file so that you can do cool stuff such as pausing and rewinding live
TV. The 'approved' method of using live TV is to use 'browse mode' so
that you can see what is on any given channel without having to change
to that channel itself. The other main answer to this query is that once
you have MythTV, you'll rarely use live TV anyway on the grounds that
all you favourite programs will be sitting on the hard drive ready to
watch.

Of course if you do have any coding skills, there's always the chance to
have a look at the code to see if channel changing can be made any
faster. You would certainly earn this FAQ writer's gratitude if you
did :)

So how many lines of code we talking about to sift to start figuring out
how to change channels faster?

Hedgehog

On Thu, 2006-11-16 at 19:36 -0500, Viitasaari wrote:
> Thanks for the response.
> 
> After I started examining my processor speed I realized that it was only
> being detected as a 1GHz when it should have been detected at around
> 2.4GHz since its an Athlon 64 3400+
> 
> I turned off the cpuspeed service which caused fedora to detect it at
> 2.4GHz however I still wondered why the kernel had been seeing a 1GHz
> CPU so I checked my BIOS settings.
> 
> I turned off the "AMD Cool & Quit" setting in my BIOS and
> restarted...bingo my CPU was detected at 2405.514MHz even while the
> cpuspeed service was running.
> 
> So I fixed that problem however, my channel change script still stutters
> like before :-(
> 
> I tried nicing the irsend commands in my script with no luck.
> 
> Is it possible that its one of my recording settings in myth.
> 
> I notice right after the stutter it comes up with a position saved
> before the channel actually starts to change.
> 
> Any help would be great.
> 
> Hedgehog
> 
> On Tue, 2006-11-14 at 13:40 -0500, Dan Wilga wrote:
> > At 7:48 AM -0500 11/14/06, Viitasaari wrote:
> > >It doesn't seem to be the DSTB since the stuttering occurs before the
> > >actual channel itself even changes.
> > >
> > >There appears to be 3 distinct parts to the stutter...one for each
> > >digit.
> > 
> > This sounds to me like it is lirc that is inducing the stutter. 
> > resolving this may be as simple as increasing the "niceness" (do a 
> > "man renice" for more info) of the lirc processes. But if you do 
> > this, you may cause some transmissions to fail, because the CPU 
> > switches away from lirc at times when it should be blasting the next 
> > bit of data.
> > 
> > Other options that may help:
> > 
> > - upgrade your kernel to one that supports the HPET_TIMER option
> > 
> > - get a blaster like either of these, which would offload the 
> > CPU-intensive stuff: http://www.mytvstore.com/product_id_004.html
> > http://www.usbuirt.com/
> > 
> > - get a faster CPU
> > 
> 
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