[pvrusb2] PAL-Plus support

[Carsten Meier]

Am Fri, 07 Nov 2008 16:55:44 +0100
schrieb Bjorn Danielsson <pvr-usb2 at dax.nu>:

> Carsten Meier <cm at trexity.de> wrote:
> >
> > I think you misunderstood me a little bit. Just to be sure we're
> > talking about the same thing: http://en.wikipedia.org/wiki/Palplus .
> > I know, that my PVRUSB2 doesn't have any decoder-hardware.
> >
> > To assemble a true 16:9-picture of a PALPlus-broacast, only the
> > lines hidden in the black letterbox-bars have to be reinserted into
> > the picture. Can that be done with the PVRUSB2?
> 
> According to that Wikipedia article, PAL-plus is a very special
> analog encoding that removes 25% of the visible scanlines and
> hides their luminance information in the color subcarrier in
> the top and bottom black sections.

Yes. The availability section of the wikipedia article is a little bit
outdated, all major broadcasters in Germany send such a signal for most
of its 16:9 content.

> In order to mix these lines
> back into sequence again you would need either hardware support
> or special software that converts the decoded video stream
> (if possible) just before displaying the frames on the screen.
> 

All that is needed is a framebuffer (which the PVRUSB2 has) and a
little bit of logic to "unhide" the lines and to put them in sequence.
(I'm not an expert on this, just my guess... ;) )
Doing that in software on decoding of the MPEG stream is not possible
because the additional information is already lost.