Did you ever find a solution to this? I'm also looking for best practices to ISO record vMix calls. Recording them directly in MultiCorder gives me (sometimes) hundreds of files I have to stitch together (understandable that that will fluctuate based on vMix call's connection/quality). But routing them thru outputs, vMix's official workaround, yields wonky frame rates PLUS uses all of my outputs (if I have 3 callers) so I no longer have an aux send to return feed the callers (for instance, I typically want to aux send all three callers a clean 4 shot instead of PGM).

I haven't tested routing the calls thru NDI and back again, possibly sending out an external render via SDI and return, or setting up a second vMix machine to only handle the callers, but curious to know if you found a solid solution(?)

Also curious to know why no vMix peeps have yet to respond here or introduce this as a new feature. Surely other people have a need to ISO record vMix calls.