[mythtv-users] Artifacts in DVB TV

[Justin Hornsby]

Matthew Phillips wrote:

> Hello all,
>
> I've just finished setting up MythTV on an EPIA M10000N system with a 
> VisionPlus DVB-T card - very happy with the results so far. Kudos to 
> the myth developers.
>
> I've been looking into one outstanding problem: the SD pictures I'm 
> getting on some channels have, either at the top or bottom of the 
> picture, a line of blank pixels which sometimes have some white 
> streaks (see top left of attached example).
>
> An enquiry to the linux-dvb mailing list indicated this is a normal 
> artifact of the WSS (Wide Screen Signaling) standard embedded into 
> analog PAL intended for digital broadcast.
>
> So, it looks like I need to have Myth crop a few lines from the top 
> and bottom of 16:9 content. However, I'm using XvMC and it (a) appears 
> filter chains can't be used with it and (b) I couldn't find any info 
> on cropping filters anyway (given they even exist).
>
> Does anyone have any idea whether there's something I can try?
>
> Cheers,
>
> Matthew.
>
I think what you're seeing is timecode which is sometimes present on the 
broadcast video - I'm not sure if it's 'proper' timecode but some 
channels have it while others don't...

Anyway you're seeing it because the broadcasters haven't bothered to 
take it out of the video stream - this is probably because you wouldn't 
normally see it on a TV because of the 5 to 10% overscan prevalent in 
most domestic TV sets.

The WSS signal isn't actually present in the PAL signal itself - the 
aspect ratio flags in the MPEG stream determine whether or not the 
receiver is to treat it as 16:9 or not.

If you're using TV-out why not take the overscan up a notch to eliminate it?

Jus.