ATEM REF usage questions.

I have a few novice questions. All of my cameras have SDI connectivity.

1. What is achieved by using the REF in?
2. What do I lose by not using the REF in?
3. Do i run SDI from the camera to a SDI DA and split that signal, one going to a input source of the ATEM and the other to the REF in of the ATEM?
4. It is a good practice to use the REF in with any ATEM live production setup?



Thanks!

Please, anyone from Blackmagic? A response?

Every switcher must have frame synchronizer on all inputs , for switching .. this delay video input with some time .. on ATEM , it is frame .. If U use Reference (into ATEM , and ALL CAMERAS!) , then ATEM will disable framesync on inputs , and u have delay near 0 msec ..

U not need to use reference ..

1. Using the REF input tells the ATEM switcher when to expect each camera to send it's first line of video (starting from the top at line 1). When your ATEM and all of your cameras are in sync and sending at the same time, the amount of output delay is reduced from 1 frame (33ms at 1080i59.94) to 1 line (0.03ms). However, ALL of your cameras must be synced using that same REF signal, otherwise the ATEM's frame synchronizers kick in and that camera gets buffered until it catches up to line 1 again, causing delay.

2. That being said, 33ms of delay isn't even noticable unless you are in an IMAG situation where the camera is being shown on a large screen / projector, but even then most people won't notice it. However, the ATEM is usually not the biggest source of delay when it comes to IMAG, as projectors typically add 4x as much delay when scaling an HD signal to their native resolution.

3. A REF signal is nothing more than an analog composite video signal that's all black (no picture) known as blackburst or tri-level sync. It is not compatible with SDI DA's, only analog video DA's. Most cameras can't generate a blackburst signal though so you'll have to get an external sync generator and plug it into the REF or genlock input of your ATEM and all of your cameras.

4. I rarely use REF on any of my live productions, including those with IMAG using multiple cameras, and I've never had a problem. Often times there's that one piece of equipment that just doesn't support genlock at all that you HAVE to get working, and so I don't bother genlocking anything, but YMMV

Hi, here's my question though:
since there is always a delay between the capture of an image and its SDI output from the camera (around two frames, at least), why would I need to send a same ref to all the cameras and the ATEM ? It doesn't make any sense to me : compared to the cameras, the ATEM is de facto offset.
Having all the cameras synced with the same ref should be enough, don't you think ?

It makes no sense to sync all sources, but not the mixer. The mixer generates its own sync indepent from the sources. So when all sources are in sync ,but their first line allways comes after mixers first line, you get a delay nearly the delay, you get without sync - nearly one frame.

Like Thomas said, if you don't sync your ATEM its internal framesyncs could be at line 700 while all of your cameras are at line 1, meaning the ATEM will sit and wait (adding delay) for your cameras to reach line 700.