[mythtv-users] HD-PVR Channel Changing Inquiry

Mike Perkins mikep at randomtraveller.org.uk
Sat Jul 17 13:15:35 UTC 2010

Larry K wrote:
> Since Comcast hosed pretty much all my unencrypted QAM (except the networks,
> of course), I just picked up an HD-PVR, another STB, and have been reading
> through all the materials I can find.
> On this wiki -> http://www.mythtv.org/wiki/Hauppauge_HD-PVR
> There is ambiguous language about how to effect channel changes.  At one
> point, it talks about how to configure a channel change script "if you care
> about changing channels".  Seems like any HD-PVR user would care about that,
> right?  Then, near the bottom, under the section entitled *"*Steps to Enable
> IR Transmitter*"*, it states that even with IR up and running, I will still
> need a channel change script.  Is this true?  If so, what is the point of
> IR?  To just power the STB up and down?  That seems hardly worth the effort
> of configuring IR.  Did I miss something here?   Anyway, if I need a
> separate channel change script, where can that be found, and if there are
> variants on that, where can I find the one most commonly used?  Do these
> channel changing scripts operate over firewire?  or over the USB cable?
>  Seems like these important details are missing from the wiki, or maybe I
> just got up late this morning :)
> I am happy to update the wiki based on whatever feedback I can get here...
There are certain assumptions being made which you're obviously not getting.

Your STB normally requires input from a remote control, no? That signal is IR 
(Infra Red).

The IR transmitter is used by myth to simulate a remote when myth needs to 
change the channel on your STB to record something. How do you think myth tells 
the IR transmitter, which is nothing more than an Infra-Red LED, what to send to 
the STB?

That's right, a channel change script. When you set this value in your tuner 
definition in mythtv-setup, myth knows to run this script whenever it needs to 
change channels on that 'tuner'. Depending on what STB - or other device - the 
tuner entry actually represents you may need one of several different channel 
change scripts. That's why it is done this way, rather than you just picking 
something from a list.

The script may just send digits out a serial port, or it may transmit a firewire 
signal, or talk to a LIRC driver, or something else. It's up to you to figure 
out what your particular setup requires and provide a suitable script.

Unfortunately, practically *everyone's* system is unique. Good luck.


Mike Perkins

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