The design of vMix Call seems to be based on a single video stream per call. One can switch the content of the video stream between Webcam and Screen-Sharing (in case of the Advanced vMix Call) but there is no possibility to ingest the Webcam and the Screen-Sharing in parallel(!) -- at least not with an acceptable user-experience.

Sure, there is the workaround to give remote callers 2(!) vMix Call URLs and teach them how to use two browser tabs in parallel (one for the Webcam, one for the Screen-Sharing). But to be honest, we really tried this in practice for many weeks. Even with good documentation this approach has a bad user-experience as non-technology affine people immediately break and even the technology-affine people hate the approach. It just is too complicated and not acceptable by users.

As in the near future I don't think this feature request will be resolved we had to really give our remote presenters a better solution at hand, a few months ago I crafted VDON Call (https://github.com/rse/vdon-call), a VDO.Ninja based vMix Call alternative to ingest 1-8 remote callers, each one with their Webcam and Screen-Sharing and all in parallel. Into the studio they are coming in with an OBS Studio instance which sends the resulting streams via NDI to vMix.

Although we're happy with the user experience and quality of VDON Call, I nevertheless would like to see vMix Call to support parallel Webcam and Screen-Sharing in the future. My recommendation is to solve the challenge on the frontend side: still use single-video stream based vMix Call type inputs inside vMix, but allow two vMix Call ids to be "merged" in the frontend for use with the Webcam and Screen-Sharing in parallel. So, the user could receive an URL with two(!) ids in it and in these cases, the frontend just uses one for the Webcam and one for the Screen-Sharing under the hood. This is compatible with the current "One Stream, One Input" design inside vMix and nevertheless gives users the experience they request.