On 21 August 2010 14:54, Pasi Kärkkäinen <pa...@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.


vdr mailing list

Reply via email to