On 21 August 2010 14:54, Pasi Kärkkäinen <pasik@xxxxxx> wrote: > 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 > > Anyone know of an open source project like this one? >From the website: ... With a PC running Linux and a recent VGA card, you can emit a real digital TV signal in the VHF band to your DVB-T set-top box. DVB-T emitters are usually very expensive professional devices. Now with a standard PC you can broadcast real DVB-T channels ! http://bellard.org/dvbt/ If you are only able to to transmit over one selected Frequency, but you can stream multiple channels together, you could drive a few SD tvs with built-in dvb-T receivers (modern tvs). I guess HD would limit it. This could be just another alternative. Infra Red would have to be dealt in a different manner. This could save on cables running through the house, by daisy chaining your coax cable like the older TVs. Ideal for content that is already in mpeg2-ts. Theunis _______________________________________________ vdr mailing list vdr@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/vdr
