obs-studio: add build for obs-ndi plugin

Note that the plugin won't do anything without the NDI library packaged, too.
I'll add that one ASAP.

pkgs/applications/video/obs-studio/fix-search-path.patch

@@ -0,0 +1,13 @@
+diff --git a/external/FindLibObs.cmake b/external/FindLibObs.cmake
+index ab0a3de..19c63ee 100644
+--- a/external/FindLibObs.cmake
++++ b/external/FindLibObs.cmake
+@@ -95,7 +95,7 @@ if(LIBOBS_FOUND)
+ 
+ 	set(LIBOBS_INCLUDE_DIRS ${LIBOBS_INCLUDE_DIR} ${W32_PTHREADS_INCLUDE_DIR})
+ 	set(LIBOBS_LIBRARIES ${LIBOBS_LIB} ${W32_PTHREADS_LIB})
+-	include(${LIBOBS_INCLUDE_DIR}/../cmake/external/ObsPluginHelpers.cmake)
++	include(external/ObsPluginHelpers.cmake)
+ 
+ 	# allows external plugins to easily use/share common dependencies that are often included with libobs (such as FFmpeg)
+ 	if(NOT DEFINED INCLUDED_LIBOBS_CMAKE_MODULES)

pkgs/applications/video/obs-studio/obs-ndi.nix

@@ -0,0 +1,39 @@
+# We don't have a wrapper which can supply obs-studio plugins so you have to
+# somewhat manually install this:
+
+# nix-env -f "<nixpkgs>" -iA obs-ndi
+# mkdir -p ~/.config/obs-studio/plugins
+# ln -s ~/.nix-profile/share/obs/obs-plugins/obs-ndi ~/.config/obs-studio/plugins/
+
+{ stdenv, fetchFromGitHub, obs-studio, cmake, qt5 }:
+
+stdenv.mkDerivation rec {
+  pname = "obs-ndi";
+  version = "4.7.1";
+
+  src = fetchFromGitHub {
+    owner = "Palakis";
+    repo = "obs-ndi";
+    rev = version;
+    sha256 = "040fkbf3f3qgqcrd3072y3zrjb4fwga8zr10jym744xd7bgyylqh";
+  };
+
+  patches = [ ./fix-search-path.patch ];
+
+  nativeBuildInputs = [ cmake ];
+  buildInputs = [ obs-studio qt5.qtbase ];
+
+  cmakeFlags = [
+    "-DLIBOBS_INCLUDE_DIR=${obs-studio}/include/obs"
+    "-DLIBOBS_LIB=${obs-studio}/lib"
+    "-DCMAKE_CXX_FLAGS=-I${obs-studio.src}/UI/obs-frontend-api"
+  ];
+
+  meta = with stdenv.lib; {
+    description = "Network A/V plugin for OBS Studio";
+    homepage = https://github.com/Palakis/obs-ndi;
+    maintainers = with maintainers; [ peti ];
+    license = licenses.gpl2;
+    platforms = with platforms; linux;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -20332,6 +20332,8 @@ in
 
   obs-wlrobs = callPackage ../applications/video/obs-studio/wlrobs.nix { };
 
+  obs-ndi = callPackage ../applications/video/obs-studio/obs-ndi.nix { };
+
   octoprint = callPackage ../applications/misc/octoprint { };
 
   octoprint-plugins = callPackage ../applications/misc/octoprint/plugins.nix { };