modules/obs-studio: optionally enable v4l2loopback (#312112)

* modules/obs-studio: optionally enable v4l2loopback

* add test

* added documentation to 24.11 changelog

nixos/modules/programs/obs-studio.nix

@@ -0,0 +1,64 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+
+let
+  cfg = config.programs.obs-studio;
+in
+{
+  options.programs.obs-studio = {
+    enable = lib.mkEnableOption "Free and open source software for video recording and live streaming";
+
+    package = lib.mkPackageOption pkgs "obs-studio" { example = "obs-studio"; };
+
+    finalPackage = lib.mkOption {
+      type = lib.types.package;
+      visible = false;
+      readOnly = true;
+      description = "Resulting customized OBS Studio package.";
+    };
+
+    plugins = lib.mkOption {
+      default = [ ];
+      example = lib.literalExpression "[ pkgs.obs-studio-plugins.wlrobs ]";
+      description = "Optional OBS plugins.";
+      type = lib.types.listOf lib.types.package;
+    };
+
+    enableVirtualCamera = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Installs and sets up the v4l2loopback kernel module, necessary for OBS
+        to start a virtual camera.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    programs.obs-studio.finalPackage = pkgs.wrapOBS.override { obs-studio = cfg.package; } {
+      plugins = cfg.plugins;
+    };
+
+    environment.systemPackages = [ cfg.finalPackage ];
+
+    boot = lib.mkIf cfg.enableVirtualCamera {
+      kernelModules = [ "v4l2loopback" ];
+      extraModulePackages = [ config.boot.kernelPackages.v4l2loopback ];
+
+      extraModprobeConfig = ''
+        options v4l2loopback devices=1 video_nr=1 card_label="OBS Cam" exclusive_caps=1
+      '';
+    };
+
+    security.polkit.enable = lib.mkIf cfg.enableVirtualCamera true;
+  };
+
+  meta.maintainers = with lib.maintainers; [
+    CaptainJawZ
+    GaetanLepage
+  ];
+}