On Fri, Aug 20, 2010 at 01:37:10AM +0300, Niko Mikkilä wrote:
> Thu, 2010-08-19 at 20:54 +0400, Goga777 wrote:
> > > Computer hardware usually cannot provide 50.000Hz, 59.940Hz or 23.976Hz
> > > outputs to your TV/Monitor. This will cause some judder on display output
> > > as MPEG/AVC input-stream is not synchronized to output framerate.
> > 
> > do you mean that all nvidia vdpau cards with existing drivers from Nvidia 
> > can't provide exact 50.000Hz,
> > 59.940Hz or 23.976Hz ??
> There is no graphics card, BD/DVD player or other standalone device that
> outputs those rates exactly. I don't know how much they deviate, but I'd
> guess it's usually something like 0.01 % (50.005 Hz instead of 50 Hz),
> as Jori said.
> However, the rate doesn't need to match exactly because the display
> device is synchronized to the video signal. The rate could be 50.1 Hz or
> maybe even 51 Hz and the display wouldn't mind. 50 fps video files would
> play slightly faster, but there would be no need to drop video frames
> because of that.
> Things are more problematic when receiving live broadcast. Then the
> display and the video source (graphics card and software) needs to be
> synchronized to the broadcast to avoid dropping or duplicating frames.
> Set-top digital television boxes and FF DVB cards do that, but most
> graphics cards/drivers can't because they aren't designed to follow an
> external time source.
> Audio playback synchronation is another issue, and somewhat difficult to
> handle properly on a PC where the audio chip's clock is almost always
> separate from the graphics card's clock. By default, many media players
> time everything according to the audio clock, and therefore they need to
> drop/duplicate video frames every now and then. The other alternative is
> to drop/duplicate audio frames or resample the audio completely.

I assume you guys are aware of projects like:

It was originally started to get perfectly synced RGB output
from a VGA card (to PAL TV), just like from FF DVB card.

I haven't really used that myself, but afaik they've been working
on making that exact synchronization (variable framerate) possible
with new HD/VGA/DVI outputs aswell.

-- Pasi

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