Update: multi camera setup
This is an update to my previous post, in case anyone is interested. (Previous post: https://www.reddit.com/r/blackmagicdesign/s/7P2EPQpLoG)
I need to record a live event from multiple angles simultaneously. I have several BMPCC 6K cameras plus an ursa 12K, and I want to record 6K/12K 2.4:1 60 fps BRAW concurrently on all of them. I would also like some kind of simple monitoring setup. And ideally some method of starting/stopping the recording on all cameras from one location. In the original post, using an ATEM was recommended, so I picked one of those up along with some long fiber HDMI cables. Everything seemed to work when I connected things for testing.
Apparently while the long fiber HDMI cables are perfectly fine for video, they are completely unreliable for camera control. I just got back from recording a live show with a four camera setup using an ATEM mini pro. The whole shebang worked great when doing a test setup in the rehearsal space, but after carrying the tripods across the hall into the theater and unrolling the cables, NONE of the camera control or timecode sync worked. Nada. Literally the only difference was the location of the equipment and the fact that the cables were unrolled, nothing else was changed. I had a couple of different 50-100 ft optical HDMI cables, video worked fine, but camera control did not work at all on any of them, both to the 6k cameras and to the ursa via the SDI converter. I suspect the sideband signals like CEC are still sent using wires, and that distance is simply too long - the signal integrity is degraded and it's also much more susceptible to picking up noise.
Long term, I am trying to decide what to do. On the one hand, I already have all the hardware, monitoring works fine, and synchronizing the clips actually wasn't bad at all since without recording control there were only a couple of clips per camera. To get camera control, I think there are only two options: switch to SDI, or find some kind of HDMI extension solution that can pass the required sideband signals reliably. Both of those I think could significantly increase the cost of the setup - SDI ATEM units seem to be more rare/expensive used, I would need more SDI converters, long SDI cables seem to be relatively expensive and I need twice as many, plus an SDI DA. And for the HDMI route, I don't even know if there are converters that would work, and 4 sets of those plus fiber would likely not be cheap.