Motivation for this change

These changes allow ffmpeg to enable the QSV encoder using intel-media-sdk. It requires that intel-media-driver is properly configured.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

Tested it works with the following commands:

$ wget https://samples.ffmpeg.org/MPEG2/dvd.mpeg
$ LIBVA_DRIVER_NAME=iHD ffmpeg -y -nostdin -hwaccel qsv -vcodec mpeg2_qsv -i dvd.mpeg -vcodec h264_qsv -preset medium -acodec copy -threads 0 out.mp4