It builds

default.nix

@@ -0,0 +1,6 @@
+let
+  pkgs = import <nixpkgs> { };
+in
+with pkgs; {
+  obs-streamfx = libsForQt5.callPackage ./obs-streamfx.nix { };
+}

obs-streamfx-force-frontend.patch

@@ -0,0 +1,13 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index acaa87c..e02bebf 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -981,7 +981,7 @@ if(REQUIRE_NVIDIA_CUDA AND D_PLATFORM_WINDOWS)
+ endif()
+ 
+ #- OBS Front-End API
+-set(HAVE_OBSFE OFF)
++set(HAVE_OBSFE ON)
+ if(REQUIRE_OBSFE)
+ 	if(${PREFIX}OBS_NATIVE)
+ 		if(TARGET obs-frontend-api)

obs-streamfx-no-download.patch

@@ -0,0 +1,25 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index acaa87c..2711adf 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -444,13 +444,13 @@ if(NOT ${PREFIX}OBS_NATIVE)
+ 	endif()
+ 
+ 	# Download libOBS
+-	download_project(
+-		PROJ libobs
+-		URL "${_DOWNLOAD_OBS_URL}"
+-		URL_HASH "${_DOWNLOAD_OBS_HASH}"
+-		DOWNLOAD_NO_PROGRESS OFF
+-		UPDATE_DISCONNECTED OFF
+-	)
++	# download_project(
++	# 	PROJ libobs
++	# 	URL "${_DOWNLOAD_OBS_URL}"
++	# 	URL_HASH "${_DOWNLOAD_OBS_HASH}"
++	# 	DOWNLOAD_NO_PROGRESS OFF
++	# 	UPDATE_DISCONNECTED OFF
++	# )
+ 
+ 	include("${libobs_SOURCE_DIR}/cmake/LibObs/LibObsConfig.cmake")
+ endif()

obs-streamfx.nix

@@ -0,0 +1,47 @@
+{ lib
+, stdenv
+, fetchFromGitHub
+, cmake
+, ffmpeg
+, libaom
+, ninja
+, pkg-config
+, qtbase
+, obs-studio
+}:
+
+stdenv.mkDerivation rec {
+  pname = "obs-streamfx";
+  version = "0.11.1";
+
+  src = fetchFromGitHub {
+    owner = "Xaymar";
+    repo = "obs-StreamFx";
+    rev = version;
+    sha256 = "KDzSrvmR4kt+46zyfLtu8uqLk6YOwS8GOI70b5s4vR8=";
+    fetchSubmodules = true;
+  };
+
+  nativeBuildInputs = [ cmake ninja pkg-config ];
+  buildInputs = [ ffmpeg libaom obs-studio qtbase ];
+
+  dontWrapQtApps = true;
+
+  cmakeFlags = with lib; [
+    "-Dlibobs_SOURCE_DIR=${obs-studio.out}/lib"
+    "-DSTRUCTURE_PACKAGEMANAGER=true"
+    "-DENABLE_UPDATER=false"
+    "-DENABLE_FRONTEND=true"
+    "-DREQUIRE_JSON=true"
+  ];
+
+  patches = [ ./obs-streamfx-force-frontend.patch ./obs-streamfx-no-download.patch ];
+
+  meta = with lib; {
+    description = "StreamFX is a plugin for OBS® Studio which adds many new effects, filters, sources, transitions and encoders - all for free! Be it 3D Transform, Blur, complex Masking, or even custom shaders, you'll find it all here.";
+    homepage = "https://s.xaymar.com/streamfx-dc";
+    maintainers = [ ];
+    license = licenses.gpl2Plus;
+    platforms = [ "x86_64-linux" ];
+  };
+}