The driver right now only supports VDPAU which is not as supported as VAAPI. Right now the only working way for VAAPI is an unofficial LIBVA driver for nvidia. With it there is a lack of a stable interface due to the EGL backend being broken as referenced right here (cuEGLStreamProducerConnect returns error 801 on 525.53 driver)
They said the fix would be incorporated into a future driver release but it has been a year and the fix has not been released yet. Will there be any plans for the bugfix to be shipped or any plans for official VAAPI support?