View Full Version : Key Channel

11-24-2003, 10:46 AM
I am having trouble selecting just the key on a composite source without the preview following it. From what I have read, I should just be able to de select the lock key check box but that does not seem to be doing the trick. What I want to have is Camera1 as my key source (green screen) with the background generator on the program to replace the green and still have the preview open so I can go to a new source. HELP!

11-24-2003, 03:55 PM
When keying remember the following:

The Main bus will be your background source.
The Key bus will be your matte source.
The Preview bus will be your fill source.

American Flag clip on main bus as background source.
Green Screen dog on key and preview bus.
If I enable the key with these steps I will see the dog keyed over the flag. Now if I unlock the key bus and move preview to a live camera, I will see the live camera in the shape of the dog keyed over the flag.

I hope this makes sense give it a try and let me know.

11-24-2003, 10:05 PM
Yeah that makes sense but my problem seems to be when I want to use the key from a live camera. In you example, you used the dog on the green. In that case, the dog is an internal source in the computer. I can select the key channel from it and the preview of another source. However, if I select a camera on the key bus, the preview follows it regardless if I have key lock on or off. I hope this makes sense. Any ideas?

11-25-2003, 04:07 PM
You've answered your own question. You can only separate the key and preview bus when the key source is internal. You can't have a separate key and preview when your key is live video.

This is a limitation of VT - there are only two live video sources in the hardware! Three live sources would mean redesigning the VT card hardware.

I too would like to see this in the next hardware along with a 64bit 66mhz bus support so the sources could all be HDTV! :D

I guess this should be sent to 'vidfeatures @ newtek.com'

11-25-2003, 10:13 PM
Thanks Gordon. I was afriad of that but I just needed someone to tell me.

11-26-2003, 06:22 AM
Is that still true if you have the breakout box. I was told that allows the toaster card to decode an additional analog source simultaneously.

11-26-2003, 07:33 AM
No the breakout box still only allows two real time analog streams to be send through the VT card into the VT software for processing.

I guess that you can have a live firewire camera as an additional live stream. However, there is latency with DV and mixing a DV camera source with analog video doesn't work too well it the subject of both cameras are the same. I haven't tried keying a DV source so don't know for sure that it works independant of the preview bus. (Due to the 5 to 1 compression of DV, you may not be happy with the DV key anyhow.)