VA-API is an API for video/image decoding/encoding acceleration implemented by libva. The files in this folder provide a fake backend for it intended to be used in tests.
It can be explicitly exercised by running e.g.:
LIBVA_DRIVER_NAME="libfake" vainfo
wherever it might be installed. See https://tinyurl.com/libva-fake-driver for its original implementation. This document is outdated but still provides the general idea for this directory.