Then we switch to iMac Pro 1,1 and everything works. You should update to 10.14.5, it’s better for AMD Gpus. Why do you call your graphic card external “egpu”, it’s outside the PC ?All EGPU ports works with iMac Pro 1,1, when we start with the changes to add IGPU as additional GPU then starts issues with second display
Look for a process called VTencoding or VTdecodind, try with a HEVC video in QuickTime. iMac 18,3 is only better in h264 because the IGPU.hmm... strage or not - when I change model:
iMac18.3 - if we compare GPU utilization with CPU - less GPU, more CPU
IMacPro1.1 - if we compare GPU utilization with CPU - more GPU, less CPU
Time for export if ~ 6min20sec.