nixos/frigate: fix ifd in libavformat soname version detection (#494548)

      environment = {

        CONFIG_FILE = "/run/frigate/frigate.yml";

        HOME = "/var/lib/frigate";

        # Extract libavformat version in the same way Docker scripts in frigate directory do. This

        # environment variable changes the flags given to `ffmpeg` improving compatibility.

        LIBAVFORMAT_VERSION_MAJOR = lib.strings.trim (

          builtins.readFile (

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

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

            ''

          )

        );

        PYTHONPATH = cfg.package.pythonPath;

      }

      // optionalAttrs (cfg.vaapiDriver != null) {

          (pkgs.writeShellScript "frigate-create-writable-config" ''

            cp --no-preserve=mode ${configFile} /run/frigate/frigate.yml

          '')

        ]

        ++ lib.optionals (!config.systemd.services.frigate.environment ? LIBAVFORMAT_VERSION_MAJOR) [

          # Extract libavformat version to enable version-dependent flags in ffmpeg

          (pkgs.writeShellScript "frigate-libavformat-major-version" ''

            echo "LIBAVFORMAT_VERSION_MAJOR=$(${cfg.settings.ffmpeg.path}/bin/ffmpeg -version | grep -Po "libavformat\W+\K\d+")" > /run/frigate/ffmpeg-env

            echo "Detected $(cat /run/frigate/ffmpeg-env)"

          '')

        ];

        EnvironmentFile = [ "-/run/frigate/ffmpeg-env" ];

        ExecStart = "${cfg.package.python.interpreter} -m frigate";

        Restart = "on-failure";

        SyslogIdentifier = "frigate";