Fix plugin failing to load on Windows (OBS 32.2+)

.gitignore

@@ -0,0 +1,6 @@
+/linux/
+/macos/
+/macos-aarch64/
+/windows/
+/gst-delayimp/
+/cross.txt

README.md

@@ -21,8 +21,10 @@ Prebuilt
 ---
 
 Experimental prebuilt 64-bit Windows plugin is available. You still require the
-official [GStreamer run-time] (MinGW version) to be installed. Make sure the
-run-time `bin` path is added to Windows's `PATH` environment.
+official [GStreamer run-time] (MinGW version) to be installed. No further setup
+is needed: the plugin locates the run-time itself via the
+`GSTREAMER_1_0_ROOT_MINGW_X86_64` environment variable the official installer
+sets, so adding it to `PATH` is not required.
 
 Experimental prebuilt macOS plugin available. You still require the GStreamer
 run-time installed via [Macports] (not Homebrew).

docker/build-windows.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+set -e
+
+export PKG_CONFIG_PATH=/c/gstreamer/1.0/x86_64/lib/pkgconfig/
+
+rm -f cross.txt
+{
+  echo "[binaries]"
+  echo "c = 'x86_64-w64-mingw32-gcc'"
+  echo "cpp = 'x86_64-w64-mingw32-g++'"
+  echo "ar = 'x86_64-w64-mingw32-ar'"
+  echo "strip = 'x86_64-w64-mingw32-strip'"
+  echo "pkgconfig = 'x86_64-w64-mingw32-pkg-config'"
+  echo "windres = 'x86_64-w64-mingw32-windres'"
+  echo ""
+  echo "[properties]"
+  echo "c_link_args = ['-static-libgcc', '-L/bin/64bit']"
+  echo "pkg_config_libdir = '/c/gstreamer/1.0/mingw_x86_64/lib/pkgconfig'"
+  echo ""
+  echo "[host_machine]"
+  echo "system = 'windows'"
+  echo "cpu_family = 'x86_64'"
+  echo "cpu = 'x86_64'"
+  echo "endian = 'little'"
+} >> cross.txt
+
+export C_INCLUDE_PATH=/
+
+rm -rf gst-delayimp
+bash docker/gen-delayimp-libs.sh /c/gstreamer/1.0/mingw_x86_64/bin gst-delayimp
+
+meson --buildtype release --cross-file cross.txt -Dpkg_config_path=/c/gstreamer/1.0/x86_64/lib/pkgconfig/ \
+	-Dgst_delayimp_dir="$(pwd)/gst-delayimp" windows
+ln -sf /c/ "windows/c:"
+ninja -C windows
+
+echo "Build complete: windows/obs-gstreamer.dll"

docker/gen-delayimp-libs.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+# Generates delay-import libraries for the GStreamer/GLib DLLs obs-gstreamer
+# directly links against on Windows, so obs-gstreamer.dll itself doesn't need
+# them resolvable at LoadLibrary time (see gstreamer.c's
+# configure_gstreamer_windows_paths()).
+set -e
+
+BIN_DIR="$1"
+OUT_DIR="$2"
+
+if [ -z "$BIN_DIR" ] || [ -z "$OUT_DIR" ]; then
+	echo "usage: $0 <gstreamer-bin-dir> <output-dir>" >&2
+	exit 1
+fi
+
+mkdir -p "$OUT_DIR"
+
+DLLS="libgstreamer-1.0-0 libgobject-2.0-0 libglib-2.0-0 libintl-8 libgstvideo-1.0-0 libgstbase-1.0-0 libgstaudio-1.0-0 libgsttag-1.0-0 libgstapp-1.0-0 libgstnet-1.0-0 libgio-2.0-0"
+
+for name in $DLLS; do
+	dll="$BIN_DIR/$name.dll"
+	if [ ! -f "$dll" ]; then
+		echo "missing $dll" >&2
+		exit 1
+	fi
+	( cd "$OUT_DIR" && gendef "$dll" )
+	x86_64-w64-mingw32-dlltool \
+		-d "$OUT_DIR/$name.def" \
+		--dllname "$name.dll" \
+		--output-delaylib "$OUT_DIR/lib${name}_delay.a"
+done

docker/mingw

@@ -13,11 +13,11 @@ RUN wget https://github.com/obsproject/obs-studio/releases/download/26.0.2/OBS-S
  && rm OBS-Studio-26.0.2-Full-x64.zip \
  && rm 26.0.2.tar.gz
 
-RUN wget https://gstreamer.freedesktop.org/data/pkg/windows/1.18.1/mingw/gstreamer-1.0-devel-mingw-x86_64-1.18.1.msi \
- && wget https://gstreamer.freedesktop.org/data/pkg/windows/1.18.1/mingw/gstreamer-1.0-mingw-x86_64-1.18.1.msi \
- && msiexec -passive -i gstreamer-1.0-mingw-x86_64-1.18.1.msi \
- && msiexec -passive -i gstreamer-1.0-devel-mingw-x86_64-1.18.1.msi \
+RUN wget https://gstreamer.freedesktop.org/data/pkg/windows/1.18.6/mingw/gstreamer-1.0-devel-mingw-x86_64-1.18.6.msi \
+ && wget https://gstreamer.freedesktop.org/data/pkg/windows/1.18.6/mingw/gstreamer-1.0-mingw-x86_64-1.18.6.msi \
+ && msiexec -passive -i gstreamer-1.0-mingw-x86_64-1.18.6.msi \
+ && msiexec -passive -i gstreamer-1.0-devel-mingw-x86_64-1.18.6.msi \
  && ln -s ~/.wine/drive_c/ /c \
- && rm gstreamer-1.0-mingw-x86_64-1.18.1.msi \
- && rm gstreamer-1.0-devel-mingw-x86_64-1.18.1.msi \
+ && rm gstreamer-1.0-mingw-x86_64-1.18.6.msi \
+ && rm gstreamer-1.0-devel-mingw-x86_64-1.18.6.msi \
  && sed -i.bak 's/c:\/projects\/repos\/cerbero.git\/1.18\/build\/dist/\/c\/gstreamer\/1.0/i' /c/gstreamer/1.0/mingw_x86_64/lib/pkgconfig/*.pc

gstreamer.c

@@ -21,6 +21,70 @@
 #include <obs/obs-module.h>
 #include <gst/gst.h>
 
+#ifdef _WIN32
+#include <windows.h>
+
+// OBS 32.2 (obsproject/obs-studio#11569) dropped %PATH% from the DLL search
+// order, breaking obs-gstreamer on Windows in two ways (issue #124):
+//  - obs-gstreamer.dll's own direct GStreamer/GLib imports could no longer
+//    be resolved at LoadLibrary time at all, so the module failed to load.
+//    Fixed by delay-loading those imports (see meson.build) so the loader
+//    doesn't need them until first use, by which point this has run.
+//  - element support DLLs pulled in later via g_module_open() could no
+//    longer be found, so register the GStreamer install's bin directory
+//    explicitly, and point GST_PLUGIN_PATH at its lib\gstreamer-1.0 so the
+//    element registry scan doesn't fall back to a guess relative to wherever
+//    the delay-loaded core DLLs happened to resolve from.
+//
+// Returns false if no usable GStreamer install was found, so the caller can
+// bail out before making any delay-loaded GStreamer call - a call that fails
+// to resolve hits the delay-load runtime's default failure handling, which
+// is not a controlled error path (see mingw-w64-crt/misc/delayimp.c).
+static bool configure_gstreamer_windows_paths(void)
+{
+	static const wchar_t *const roots[] = {
+		L"GSTREAMER_1_0_ROOT_MINGW_X86_64",
+		L"GSTREAMER_1_0_ROOT_MSVC_X86_64",
+	};
+
+	SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);
+
+	for (size_t i = 0; i < sizeof(roots) / sizeof(roots[0]); i++) {
+		wchar_t root[MAX_PATH];
+		DWORD len = GetEnvironmentVariableW(roots[i], root, MAX_PATH);
+		if (len == 0 || len >= MAX_PATH - 32)
+			continue;
+		if (root[len - 1] != L'\\') {
+			wcscat(root, L"\\");
+			len++;
+		}
+
+		wchar_t bin_path[MAX_PATH];
+		wcscpy(bin_path, root);
+		wcscat(bin_path, L"bin");
+
+		wchar_t core_dll[MAX_PATH];
+		wcscpy(core_dll, bin_path);
+		wcscat(core_dll, L"\\libgstreamer-1.0-0.dll");
+		if (GetFileAttributesW(core_dll) == INVALID_FILE_ATTRIBUTES)
+			continue;
+
+		if (!AddDllDirectory(bin_path))
+			continue;
+
+		if (GetEnvironmentVariableW(L"GST_PLUGIN_PATH", NULL, 0) == 0) {
+			wchar_t plugin_path[MAX_PATH];
+			wcscpy(plugin_path, root);
+			wcscat(plugin_path, L"lib\\gstreamer-1.0");
+			SetEnvironmentVariableW(L"GST_PLUGIN_PATH", plugin_path);
+		}
+		return true;
+	}
+
+	return false;
+}
+#endif
+
 extern const char *obs_gstreamer_version;
 
 OBS_DECLARE_MODULE()
@@ -82,6 +146,16 @@ bool obs_module_load(void)
 {
 	guint major, minor, micro, nano;
 
+#ifdef _WIN32
+	if (!configure_gstreamer_windows_paths()) {
+		blog(LOG_ERROR,
+		     "[obs-gstreamer] Could not locate a GStreamer runtime install (checked "
+		     "GSTREAMER_1_0_ROOT_MINGW_X86_64 and GSTREAMER_1_0_ROOT_MSVC_X86_64). Install the official "
+		     "GStreamer Windows runtime: https://gstreamer.freedesktop.org/download/");
+		return false;
+	}
+#endif
+
 	gst_version(&major, &minor, &micro, &nano);
 
 	blog(LOG_INFO, "[obs-gstreamer] build: %s, gst-runtime: %u.%u.%u", obs_gstreamer_version, major, minor, micro);

meson.build

@@ -35,6 +35,44 @@ if host_machine.system() == 'darwin'
   name_suffix = 'so'
 endif
 
+gst_deps = [
+  dependency('gstreamer-1.0', version : '>=1.16.0'),
+  dependency('gstreamer-video-1.0'),
+  dependency('gstreamer-audio-1.0'),
+  dependency('gstreamer-app-1.0'),
+  dependency('gstreamer-net-1.0'),
+]
+
+link_deps = [obs_dep] + gst_deps
+extra_link_args = []
+
+if host_machine.system() == 'windows'
+  # obs-gstreamer.dll must be loadable by OBS even when the GStreamer/GLib
+  # runtime it links against isn't resolvable yet (OBS 32.2 dropped %PATH%
+  # from DLL search, see gstreamer.c's configure_gstreamer_windows_paths()).
+  # Take compile args from pkg-config as usual, but link against pre-generated
+  # delay-import archives (docker/gen-delayimp-libs.sh) instead of the normal
+  # eagerly-loaded import libraries.
+  gst_compile_deps = []
+  foreach d : gst_deps
+    gst_compile_deps += d.partial_dependency(compile_args : true, includes : true)
+  endforeach
+  link_deps = [obs_dep] + gst_compile_deps
+
+  delayimp_dir = get_option('gst_delayimp_dir')
+  if delayimp_dir == ''
+    error('gst_delayimp_dir must be set when building for Windows (see docker/gen-delayimp-libs.sh)')
+  endif
+
+  foreach name : ['libgstreamer-1.0-0', 'libgobject-2.0-0', 'libglib-2.0-0', 'libintl-8',
+                   'libgstvideo-1.0-0', 'libgstbase-1.0-0', 'libgstaudio-1.0-0', 'libgsttag-1.0-0',
+                   'libgstapp-1.0-0', 'libgstnet-1.0-0', 'libgio-2.0-0']
+    extra_link_args += [delayimp_dir / 'lib' + name + '_delay.a']
+  endforeach
+
+  extra_link_args += ['-ldelayimp']
+endif
+
 shared_library('obs-gstreamer',
   'gstreamer.c',
   'gstreamer-source.c',
@@ -48,13 +86,7 @@ shared_library('obs-gstreamer',
   ),
   name_prefix : '',
   name_suffix : name_suffix,
-  dependencies : [
-    obs_dep,
-    dependency('gstreamer-1.0', version : '>=1.16.0'),
-    dependency('gstreamer-video-1.0'),
-    dependency('gstreamer-audio-1.0'),
-    dependency('gstreamer-app-1.0'),
-    dependency('gstreamer-net-1.0'),
-  ],
+  dependencies : link_deps,
+  link_args : extra_link_args,
   install : true,
 )

meson_options.txt

@@ -0,0 +1,2 @@
+option('gst_delayimp_dir', type : 'string', value : '',
+  description : 'Directory containing delay-import archives generated by docker/gen-delayimp-libs.sh (Windows only)')