[vdr] More thoughts on Matrox TV out with interlaced programmes

[Tony Houghton <h@realh.co.uk>]

I've been doing a bit of brainstorming about displaying interlaced
programmes on Matrox TV out with the field parity feature and realised
this could introduce another problem. As well as having to keep the
sound and picture in sync with each other at the rate at which they're
being broadcast, AIUI the picture has to be kept in sync with the card's
vblank interrupts, otherwise the field parity won't work properly. Since
I don't think there is any way of controlling the graphics card's clock
this would probably mean having to skip or repeat (pairs of) frames
every so often, and the best we can hope for is that Matrox's quality
means the graphics card's clock is sufficiently accurate to prevent that
from happening too often [1]. Has this been taken into account in the
softdevice plugin?

There's also the issue of recordings vs live TV. In theory it should be
possible to avoid the above problem with recordings by reading the file
at a rate to suit the graphics card's clock. But it looks as if a
cReceiver has no choice but to receive the data at the rate VDR sends
it. Obviously for live TV that would be determined by the broadcast, but
I presume for recordings VDR uses a system clock. If that's separate
from the clock used by the graphics card and they drift much, it would
get ugly. In case there is a potential problem there, would it be
possible for cReceiver to be extended so that a plugin can feed back to
VDR to moderate the rate at which data is sent if possible?

[1] I think the tolerance would have to be within a small fraction of a
percent to stop it getting ugly. Otherwise field parity just isn't worth
using after all for live TV - and if it can't be used there, there's not
much point in going to the trouble of supporting it for recordings
either - and I'll have to get a faster CPU for software deinterlacing
:-(.

-- 
TH * http://www.realh.co.uk