[mythtv-users] Re: Wits end

Bruce Markey bjm at lvcm.com
Fri Dec 30 16:32:54 EST 2005

Rodney D. Myers wrote:
> I plan on heading into tonn tomorrow to get an s-video cable
> nonetheless, but any idea as to what is happening?

If you are using an external device with it's own tuner and connecting
it by coax to the tuner of the capture card, the capture card tuner
needs to remain on channel 3 (or 4 is the other common channel) no
matter which channel the external device is tuned to. Myth has an
option for this situation.

First, establish if there is an over the air channel in your area
for three or four. Unless you are midway between metropolitan areas,
there will normally be one or the other and not both. Set the output
of the external box to the unused channel. I'll assume you've gotten
this right but if there is a local channel 3, switch the box to 4.

Run mythtv-setup. Go to Input connections and choose the tuner input.
Select the Video source. Because you don't have an IR blaster and
script yet, use "/bin/true" and the "External channel change command"
If you had left this blank, that may have been the problem. If the
external command is set and you are using the coax tuner input, set
the "Preset tuner to channel" to match the output channel of the
external box. The effect will be that when you change to channel
23, "/bin/true 23" will return success and the tuner on the card
will stay on the preset channel.

You will get a better picture by using s-video. The cable keeps the
luma and chroma signals separate and only caries video. The external
box will have red and white audio output RCA jacks. Your card most
likely has a 1/8" stereo audio input jack. Therefore, you will need
to get a two female RCA to 1/8" stereo jack adapter along with a
stereo 2 wire RCA cable for the length you'll need if you don't have
one already. NOTE: the adapter should have color coded RCA connectors
(normally red and white) and 3 contacts on the 1/8" jack. There are
also splitters or combiners with two unmarked RCA to a mono 1/8"
jack. This is not what you want. The adapter you what should look
something like one of these:


When you get the s-video wired up, run mythtv-setup again. Set the
tuner input video source to "(None)" to disable it. Set the video
source for the s-video, "/bin/true" for your temporary external
command, and leave the preset blank.

--  bjm

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