so after some searching around it seems i found the culprit in my case:
searching for av_interleaved_write_frame(): Unknown error i found this site https://stackoverflow.com/questions/18274693/av-interleaved-write-frame-unknown-error-when-streaming-webm and the description from one of the answers said that the error was caused by other programs accessing the port, so i opened powershell and ran the netstat command.
Not much out of the ordinary, but i saw the mbamservice.exe, which is form malwarebytes premium, that i run on the pc.
Quit Malwarebytes, and the errors seem to have gone. Normally, it took a maximum of ~20 minutes until the error showed up, with malwarebytes quit I’m 40 minutes running on a movie and still hardware (hw) transcoding.
Will keep watching this though, maybe I just got lucky now and its a coincidence
