Add libplacebo GPU module with render and shader filters

New module 'placebo' providing GPU-accelerated video processing via
libplacebo. Includes two filters:

- placebo.render: GPU scaling, debanding, dithering, and tonemapping
  with quality presets (fast/default/high_quality)
- placebo.shader: Custom mpv-compatible .hook shader support

Backend priority: D3D11 (Windows) -> Vulkan -> OpenGL.
Vulkan loader is dynamically loaded on Windows when libplacebo is
built without vk-proc-addr support.

Features:
- Singleton GPU context with thread-safe access
- Shader cache persistence
- Multiple scaling algorithms (ewa_lanczos, lanczos, mitchell, etc.)
- Tone mapping (auto, clip, mobius, reinhard, hable, bt.2390, spline)
- Graceful fallback to passthrough when no GPU is available

The module is enabled by default but skipped automatically when
libplacebo is not installed.

Author: D-Ogi

.github/workflows/static-code-analysis.yml

@@ -19,6 +19,9 @@ jobs:
         --library=cppcheck.cfg
         --suppress=ctuOneDefinitionRuleViolation
         --suppress=syntaxError:src/modules/xml/common.c
+        --suppress=syntaxError:src/modules/placebo/filter_placebo_render.c
+        --suppress=syntaxError:src/modules/placebo/filter_placebo_shader.c
+        --suppress=syntaxError:src/modules/placebo/gpu_context.c
     steps:
       - uses: actions/checkout@v4
       - name: Install Cppcheck

CMakeLists.txt

@@ -33,6 +33,7 @@ option(MOD_NORMALIZE "Enable Normalize module (GPL)" ON)
 option(MOD_OLDFILM "Enable Oldfilm module" ON)
 option(MOD_OPENCV "Enable OpenCV module" OFF)
 option(MOD_MOVIT "Enable OpenGL module" ON)
+option(MOD_PLACEBO "Enable libplacebo GPU module" ON)
 option(MOD_PLUS "Enable Plus module" ON)
 option(MOD_PLUSGPL "Enable PlusGPL module (GPL)" ON)
 option(MOD_QT6 "Enable Qt6 module (GPL)" ON)
@@ -303,6 +304,15 @@ if(MOD_MOVIT)
   list(APPEND MLT_SUPPORTED_COMPONENTS movit)
 endif()
 
+if(MOD_PLACEBO)
+  pkg_check_modules(libplacebo IMPORTED_TARGET libplacebo)
+  if(libplacebo_FOUND)
+    list(APPEND MLT_SUPPORTED_COMPONENTS placebo)
+  else()
+    set(MOD_PLACEBO OFF)
+  endif()
+endif()
+
 if(MOD_PLUS)
   pkg_check_modules(libebur128 IMPORTED_TARGET libebur128)
   list(APPEND MLT_SUPPORTED_COMPONENTS plus)
@@ -568,6 +578,7 @@ add_feature_info("Module: Normalize" MOD_NORMALIZE "")
 add_feature_info("Module: Oldfilm" MOD_OLDFILM "")
 add_feature_info("Module: OpenCV" MOD_OPENCV "")
 add_feature_info("Module: Movit" MOD_MOVIT "")
+add_feature_info("Module: Placebo" MOD_PLACEBO "")
 add_feature_info("Module: Plus" MOD_PLUS "")
 add_feature_info("Module: PlusGPL" MOD_PLUSGPL "")
 add_feature_info("Module: Qt6" MOD_QT6 "")

src/modules/CMakeLists.txt

@@ -48,6 +48,10 @@ if(MOD_MOVIT)
   add_subdirectory(movit)
 endif()
 
+if(MOD_PLACEBO)
+  add_subdirectory(placebo)
+endif()
+
 if(MOD_PLUS)
   add_subdirectory(plus)
 endif()

src/modules/placebo/CMakeLists.txt

@@ -0,0 +1,55 @@
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(libplacebo IMPORTED_TARGET libplacebo)
+if(NOT libplacebo_FOUND)
+  return()
+endif()
+
+add_library(mltplacebo MODULE
+  factory.c
+  gpu_context.c gpu_context.h
+  filter_placebo_render.c
+  filter_placebo_shader.c
+)
+
+file(GLOB YML "*.yml")
+add_custom_target(Other_placebo_Files SOURCES
+  ${YML}
+)
+
+include(GenerateExportHeader)
+generate_export_header(mltplacebo)
+target_compile_options(mltplacebo PRIVATE ${MLT_COMPILE_OPTIONS})
+target_include_directories(mltplacebo PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
+target_link_libraries(mltplacebo PRIVATE mlt PkgConfig::libplacebo)
+
+# Only link D3D11 if libplacebo was built with D3D11 support
+include(CheckCSourceCompiles)
+set(CMAKE_REQUIRED_INCLUDES ${libplacebo_INCLUDE_DIRS})
+check_c_source_compiles("
+  #include <libplacebo/config.h>
+  #if !defined(PL_HAVE_D3D11) || !PL_HAVE_D3D11
+  #error no d3d11
+  #endif
+  int main(void) { return 0; }
+" PLACEBO_HAS_D3D11)
+if(PLACEBO_HAS_D3D11)
+  target_link_libraries(mltplacebo PRIVATE d3d11 dxgi)
+endif()
+if(WIN32)
+  target_link_libraries(mltplacebo PRIVATE shell32 ole32)
+endif()
+
+if(MSVC)
+  target_link_libraries(mltplacebo PRIVATE PThreads4W::PThreads4W)
+endif()
+
+set_target_properties(mltplacebo PROPERTIES
+  LIBRARY_OUTPUT_DIRECTORY "${MLT_MODULE_OUTPUT_DIRECTORY}")
+
+install(TARGETS mltplacebo LIBRARY DESTINATION ${MLT_INSTALL_MODULE_DIR})
+
+install(FILES
+  filter_placebo_render.yml
+  filter_placebo_shader.yml
+  DESTINATION ${MLT_INSTALL_DATA_DIR}/placebo
+)

src/modules/placebo/factory.c

@@ -0,0 +1,53 @@
+/*
+ * factory.c -- module registration for libplacebo filters
+ * Copyright (C) 2025 D-Ogi
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include "mltplacebo_export.h"
+#include <framework/mlt.h>
+#include <limits.h>
+#include <string.h>
+
+extern mlt_filter filter_placebo_render_init(mlt_profile profile,
+                                             mlt_service_type type,
+                                             const char *id,
+                                             char *arg);
+extern mlt_filter filter_placebo_shader_init(mlt_profile profile,
+                                             mlt_service_type type,
+                                             const char *id,
+                                             char *arg);
+
+static mlt_properties metadata(mlt_service_type type, const char *id, void *data)
+{
+    char file[PATH_MAX];
+    snprintf(file, PATH_MAX, "%s/placebo/%s", mlt_environment("MLT_DATA"), (char *) data);
+    return mlt_properties_parse_yaml(file);
+}
+
+MLTPLACEBO_EXPORT MLT_REPOSITORY
+{
+    MLT_REGISTER(mlt_service_filter_type, "placebo.render", filter_placebo_render_init);
+    MLT_REGISTER(mlt_service_filter_type, "placebo.shader", filter_placebo_shader_init);
+    MLT_REGISTER_METADATA(mlt_service_filter_type,
+                          "placebo.render",
+                          metadata,
+                          "filter_placebo_render.yml");
+    MLT_REGISTER_METADATA(mlt_service_filter_type,
+                          "placebo.shader",
+                          metadata,
+                          "filter_placebo_shader.yml");
+}