nixos/frigate: use upstream grep command for LIBAVFORMAT_VERSION_MAJOR

        LIBAVFORMAT_VERSION_MAJOR = lib.strings.trim (

          builtins.readFile (

            pkgs.runCommandLocal "libavformat-major-version" { } ''

              ${cfg.settings.ffmpeg.path}/bin/ffmpeg -version 2>&1 \

                | sed -n 's/.*libavformat[[:space:]]*\([0-9]*\).*/\1/p' \

                | head -1 > $out

              ${cfg.settings.ffmpeg.path}/bin/ffmpeg -version | grep -Po "libavformat\W+\K\d+" > $out

            ''

          )

        );