Video Problem, black screen, no preview, no Video Calls

Question

Hi there,

I try to get H.264 Video to work on different phones. S9+, S6 and S5. The problem is, that when I switch to Video Calls the screen turns black. Audio is still working, but no Video is send or a camerapreview on cellphone screen was shown. Zoiper use all permissions and Android Versions 7 up to 8 are in use.

I can use H.264 Video in my sip network, because my doorbell sends H.264 Video codec and it is shown.

Thanks for your help