[mythtv-users] Artifacts in DVB TV
mythtv at mattp.name
Tue Mar 15 09:49:19 UTC 2005
On 15/03/2005, at 12:42 PM, Justin Hornsby wrote:
> 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?
> 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?
The problem happens when I'm playing 16:9 on my 4:3 TV where the black
bars at the top are a given unless I want to crop the picture. I
wouldn't bother with it, but the lines are exactly the right thickness
to flicker nastily on an interlaced TV display (they look totally
innocuous on a digital display of course).
I'll write a letter to the lazy Australian broadcasters and ask them to
get with the program ;)
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