[mythtv-users] Jittery Picture and Per-channel Image Cropping?

Michael T. Dean mtdean at thirdcontact.com
Fri Sep 28 19:31:47 UTC 2007

On 09/27/2007 10:23 PM, Eric Robinson wrote:
> So this is kind of two problems but I'm thinking they may be related.
> 1) I have a few channels where the image is jittery, or shaky.  Is there
> a way to fix this?  Perhaps it's not tuned exactly right...?

You sure it's not an issue of insufficient bitrate in your recording

> 2) I have one channel that seems to have a one or two pixel wide
> flickery 'bar' at the top of the video.  I also have one channel with a
> similar vertical version of the 'bar'.  Is there away to crop those
> channels so that it doesn't produce the eye-sore?

This case (with the horizontal bar at the top) is likely just VBI data. 
Sometimes with even digital channels, the provider incorrectly digitizes
shows and puts this at the top.  On analog channels, it's often there,
but is supposed to be "hidden" by overscan.  Overscan would "fix" it for
you (you wouldn't see it and would see a picture more like what you're
supposed to see).  Alternatively, you could use the crop filter (
http://mythtv.org/docs/mythtv-HOWTO-10.html#ss10.4 ), but note that it
crops in increments of 8 pixels.

> I saw in the Channel Setup area of mythtv-setup a slider for frequency
> fine-tuning... what exactly does that do?  Would it help in either of
> the above cases?

Most likely you shouldn't need any fine-tuning.  The hardware
fine-tuning mechanism inside the hardware tuner module will probably
just auto-correct to the same tuned frequency it's tuning without any
fine-tune settings.  Feel free to play with it, though.


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