Our "trick" to get separate SDI-Outs of single vMix Callers out of vMix is running the whole project in 2160p, arrange a 2x2 matrix of 4 callers on a fullscreen output and then use a AJA HA5-4K to split the quadrants in 4 separate 1080p SDI outs. You can get 8 SDI outs by using the two fullscreen outputs this way.

The compromise you have to make is that the whole project has to run in 4k. This is ok for a few callers - all machines we have can handle that, but for bigger projects with 50-70 or even more inputs running the whole thing in 2160p50 instead of 1080p50 is not an option. It would be great if there was an option in vMix to get 4 inputs in a 2x2 layout out via HDMI in 4k resolution (one of the Fullscreen outputs) on a 1080p or 720p project. This would be awesome.

Connecting a 4k monitor to the HDMI output and sending out a 2x2 layout on a 1080p project results in a blurry picture since the 4 1080p inputs on the layers are downscaled to 540 pixels and then the whole new input is upscaled from 1080p to 2160p again on the HDMI out.

From my understanding, all the data is already in the GPU and there should no additional data transfers be needed, so this should not create additional load to the system or GPU at all. This should be no different than upscaling a 1080p input on my 4k HDMI output...

We need the additional outs for additional downstage monitors with speaker clocks etc... NDI is just too much latency and only 2 more outputs anyway...