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: http://frc.easy-vdr.de/ 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 _______________________________________________ vdr mailing list vdr@linuxtv.org http://www.linuxtv.org/cgi-bin/mailman/listinfo/vdr
