[mythtv-users] Fuzz in my video output

[Brian Wood]

On Jun 19, 2006, at 4:18 PM, Daniel Kristjansson wrote:

> On Mon, 2006-06-19 at 16:02 -0600, Brian Wood wrote:
>>>> It's probably being transmitted intentionally, it is data, in the
>>>> digital equivalent of the vertical blanking interval.
>>>> Usually most TVs overscan just a bit to prevent this showing up in
>>>> the picture.
>>> I'm viewing this on my monitor (Dell 24 inch 2405FPW LCD).. have
>>> you heard of it happening on monitors as well?
>> Especially on monitors, because they normally do not overscan at all.
>> I think Myth has some overscan settings in it, I'm not by my machine
>> at the moment and so can't check.
>> But I want to be sure this is what the problem is, I've never watched
>> QAM channels enough to notice if there is usually a bunch of data at
>> the top.
>> Can anybody else confirm this ? The description certainly sounds like
>> what data would look like in that position.
>
> I can confirm this is VBI data. This happens when the broadcaster or
> cable operator captures the entire frame of a NTSC stream. If you use
> either of the computer inputs on the monitor it won't do any overscan
> so you will see this data. MythTV can scale the video up a bit to hide
> this data. This one of the playback options and is called "overscan"
> in 0.19 and 0.19-fixes.


Thanks, I just wanted to confirm that, because I went and checked a  
recording I'd made of a couple of QAM channels and I saw only about 1  
or 2 lines of what looked like data, not "half an inch".

I suppose it is probably inserted by the cable operator and different  
systems and equipment have differing needs to insert varying amounts  
of data, probably there to help the cable operators perpetrate their  
nefarious schemes.