[mythtv-users] Any hope for 1080i content at 1080i with nVidia?

Steve Smith st3v3.sm1th at gmail.com
Mon Jul 30 14:20:09 UTC 2007


On 30/07/07, Mark Kendall <mark.kendall at gmail.com> wrote:
>
> On 7/30/07, Steve Smith <st3v3.sm1th at gmail.com> wrote:
> > It seems the simple problem is that FRAME sync (rather than FIELD sync)
> just
> > isn't working
> > somewhere along the line...
>
> > The fact that we do means that the syncing system is not working
> somewhere
> > along the line, maybe it's the card, maybe the nvidia driver, maybe Myth
> ...
> > does anyone know?
>
> It's not mythtv. As far as I can tell, there is no method available
> (with linux at least) to  sync to a specific field -  and I spent a
> lot of time looking :)
>
> Mark
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>

Erm we don't need to sync to a specified field just the beginning of the
frame (I suppose that's similar).
So in the case of a "PAL" signal that's 25hz at the beginning of the FRAME.
The video card should know when it's starting each frame, if it doesn't it's
doing something very odd with interlaced output.
Basically if we are outputting an interlaced signal from the card, programs
shouldn't really need to know. In the case of my 576i signal as far as myth
is concerned it should think it's a 720x576 at 25hz display, and receive sync
at the beginning of each frame.

(Looking at the specs for
NTSC signals it should always then send the TOP field first followed by the
BOTTOM, the
spec uses a slightly altered sync timing between the two fields to set
whether it's top or bottom so the TV/display will be able to show top
followed by bottom correctly.)

The fact that you can't sync to a specified field in linux leads me to think
that either:
   a) The video card/driver is sending FIELD sync i.e. 50Hz for PAL
   b) The video card/driver is sending FRAME sync but not always at the
beginning of the frame. i.e. it's a 25hz signal on a field sync boundary
that's sometimes the same as frame sync and sometimes the in-between field
sync.
  c) The video card/driver is sending the correct FRAME sync but something
else is messing up.

Either way it's a bug, whether it's fixable is another matter...

(Note that this only applies to driving the display using the CRT, DVI etc
ports NOT using S-VIDEO/Composite as the TV out chips seem to have their own
bizarre timing rules).

Cheers

Steve
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