[vdr] VDR with 50Hz clock output

martinez martinez at embl.de
Mon Aug 23 09:28:59 CEST 2010


Looking at the circuit diagram for the vga2scart cable. at http://vga2scart.gw90.de/cable/vga2scart/
What pins need to be mapped on the scart to include also sound (for a complete vga+ stereo out > SCART cable)


Message: 1
Date: Sat, 21 Aug 2010 15:54:03 +0300
From: Pasi K?rkk?inen <pasik at iki.fi>
Subject: Re: [vdr] Advice on new motherboard, xineliboutput, vdpau,
	hdmi	video & audio, etc.
To: vdr at linuxtv.org
Message-ID: <20100821125403.GW2804 at reaktio.net>
Content-Type: text/plain; charset=iso-8859-1

On Fri, Aug 20, 2010 at 01:37:10AM +0300, Niko Mikkil? 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


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