On 21 August 2010 14:54, Pasi Kärkkäinen pasik@iki.fi 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 !
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