DV Screen output

6 replies [Last post]
mark williams
Joined: Aug 24 2002

Is there a way (or software to allow) a firewire card to output screen activity as a digital signal? If this was then recorded onto DV tape, it should allow, with minimum processing overhead, the highest quality smooth screen capture.

Has a software company already achieved this?

Joined: Jun 1 2002

Hi Mark. I may be missing the point of your question but as I see it this is quite normal pratice anyhow. Once I have got something captured on screen I can simply output it back through the same firewire port it came in on to DV tape.

If that is not what you are asking can you please give more detail. Also DV is DV and so what ever your method its quality is constant.


Alan Roberts at work
Joined: May 6 1999

I guess that mark wants to capture the entire PC screen and output it as a real-time DV data stream. Problem there is that the screen size is never 720x576 (mine's 1152x864), so something would have to be downconverting it first apart from then having to DV compress it. Plus, the DV frame rate is 25fps (50 fields/sec interlaced) and PC displays run all sorts of silly rates. All that's a pretty big overhead for any PC to do.

I reckon the answer's "no", there's no hardware or software to do it, and not likely to be either.

mooblie's picture
Joined: Apr 27 2001

Alan, maybe some software could:

- take a PC with a screen set to 640x480 pixels and 50, 75 or 100Hz refresh rate,
- add a black border to bring it up to 720x576,
- sub-sample to 25Hz, and then
- compress to a DV stream in realtime?

Maybe the need for "non-square-DV-pixels" could be ignored?

I can see two problems:
1 - the PC would strictly have to have a stereo audio 48Khz 16-bit A-to-D as well, and
2 - the PC actually has to do some other work at the same time! - i.e. run some other software for anything to be moving on the screen!

Martin - DVdoctor in moderation. Everyone is entitled to my opinion.

Alan Roberts at work
Joined: May 6 1999

Yeah, it could do all that if someone wrote the software and if Mark's prepared to work in VGA mode. But even so, the cpu overhead to create the DV stream would be pretty high. We're talking of real-time rendering here, my P4 running at 1.7GHz can't do that, even with nothing running in the background (it's effectively rendering a series of still frames, try that in any DV NLE to see how long it takes). So it would have to be a hardware coder, and that means we're talking of a high-end DV card like some of the Canopus stuff.

I still reckon it isn't on, from a practical perspective.

Joined: Jul 19 2002

Not sure exactly what the thread originator wants to do but take a look at some of the Matrox "Dual Head" cards, I believe that you can output a copy of the main screen, (in any res you want) to the second video socket or in some of the cards a TV or S Video output.

Do check carefuly on the Matrox site as I am sure they have cards that will output video as well as (computer digital) but dont quote me.


Joined: Aug 31 2002

SyntheticAperture make software for outputting Photoshop or music programme video output to firewire