[mythtv-users] External Channel Change Script for DVB cards

Colin Albert colintrebla at gmail.com
Sat Oct 29 14:39:42 UTC 2011

I am reviving and old thread.  It relates to an issue that is a problem
for me and will be an ever increasing problem as Cable companies
continue to adopt SDV.

The problem: I have a QAM card and want to build a MythTV box instead of
using the cable company's (busted/worthless) DVR. The cable company uses
SDV, so QAM is limited to OTA locals.

My solution: get a set top box from the cable company, hook it to my
MythTV.  Use a External channel change script to change channels so that
the box is requesting the channel that I want. Then change the channel
on the QAM card to that channel.

Let me know if there is a simpler solution (without buying additional

Here is the original issue from an old thread...  Technically similar to
my issue.

> Hi, I've been building my dream *MythTV* setup for several months and
> off one issue at a time, but this one has me stumped. 
> My backend has a couple of pcHDTV HD-5500 cards and a Haupauge PVR-350. I 
> plan to use the HD-5500's to receive OTA HD, and connect the PVR-350 to my 
> old DirecTV box. I just put up a new antenna and *Channel* Master 9521A 
> rotor. This rotor has a remote and can be programmed to move to a 
> predefined direction. (I live in the boondocks of NW Ohio and am 60+ miles 
> from any major TV towers, so I need to move the antenna to get a strong 
> signal.) I have created a script ( Antenna_GoToChannel.sh ) to run an IR 
> Blaster to *change* the antenna to the proper preset position. It works
> from the command line. 
> Now I wanted to have *MythTV* call my script when I changed channels,
but I 
> see no "*External* *channel* *change* command" for the HD-5500 cards,
only for the 
> PVR-350. 
> I searched the Archives on Gossamer and someone said there was none
for *DVB* 
> cards, only V4L cards. 
> So I have two questions: 
> 1) Is there really no place to call my script, or am I missing 
> something? 
> 2) If not, why? Not complaining, I just want to understand. 
> Thanks, Keith 
You won't see any *channel* *change* scripts for *DVB* cards since, as
they are 
plugged into the computer which is running the back
end, *Mythtv* can *change* the 
*channel* directly. Providing, of course, it knows which card it is, and
specified that, anyway, in the setup procedure. 

If Mythbackend sees an *external* *channel* *change* script in the
settings, it will 
assume that you are using some kind of *external* box, and thus won't
need to 
*change* the *channel* of the internal tuner. For example, with a
PVR-350, you can 
plug the output of a set top box (or satellite tuner, etc) into the S-Video 
input. That's probably why you find references to PVR-350
and *external* *channel* 
*change* scripts. 

As far as I know, you have an unusual setup. I suspect that the main
you will get here will be to install another aerial, and connect it to a
HD-5500 card. 

However, it is possible that someone else may have another solution to your 
problem which won't involve buying more hardware. 
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