I had the same error messages, it turned out that, while hardware acceleration was working for the cameras, it did not work for the web streaming. I had to turn it off on the streaming profile.
I have this problem only with Reolink Cameras (410 and 420). If I choose my GeForce 1070 GPU for Hardware Acceleration, it works fine but if I switch to the Intel UHD 630 (Coffee Lake) on the same system, it fails and disables the Hardware Acceleration.
I have other Cams (Ubiquiti and Hikvision)...