Add thumbnail support via ffmpeg API (incomplete

extensions/cmake/FindSWSCALE.cmake

@@ -0,0 +1,32 @@
+find_package(PkgConfig)
+if (PkgConfig_FOUND)
+    pkg_check_modules(PC_SWSCALE QUIET IMPORTED_TARGET GLOBAL libswscale)
+endif()
+
+if (PC_SWSCALE_FOUND)
+    set(SWSCALE_FOUND TRUE)
+    set(SWSCALE_VERSION ${PC_SWSCALE_VERSION})
+    set(SWSCALE_VERSION_STRING ${PC_SWSCALE_STRING})
+    set(SWSCALE_LIBRARYS ${PC_SWSCALE_LIBRARIES})
+    if (USE_STATIC_LIBS)
+        set(SWSCALE_INCLUDE_DIRS ${PC_SWSCALE_STATIC_INCLUDE_DIRS})
+    else()
+        set(SWSCALE_INCLUDE_DIRS ${PC_SWSCALE_INCLUDE_DIRS})
+    endif()
+    if (NOT SWSCALE_INCLUDE_DIRS)
+        find_path(SWSCALE_INCLUDE_DIRS NAMES libswscale/swscale.h)
+    endif()
+    if (NOT TARGET SWSCALE::SWSCALE)
+        add_library(SWSCALE::SWSCALE ALIAS PkgConfig::PC_SWSCALE)
+    endif()
+else()
+    message(FATAL_ERROR "failed.")
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(SWSCALE
+    FOUND_VAR SWSCALE_FOUND
+    REQUIRED_VARS
+        SWSCALE_LIBRARYS
+    VERSION_VAR SWSCALE_VERSION
+)