Add thumbnail support via ffmpeg API (incomplete

extensions/cmake/FindAVFORMAT.cmake

@@ -0,0 +1,33 @@
+find_package(PkgConfig)
+if (PkgConfig_FOUND)
+    pkg_check_modules(PC_AVFORMAT QUIET IMPORTED_TARGET GLOBAL libavformat)
+endif()
+
+if (PC_AVFORMAT_FOUND)
+    set(AVFORMAT_FOUND TRUE)
+    set(AVFORMAT_VERSION ${PC_AVFORMAT_VERSION})
+    set(AVFORMAT_VERSION_STRING ${PC_AVFORMAT_STRING})
+    set(AVFORMAT_LIBRARYS ${PC_AVFORMAT_LIBRARIES})
+    if (USE_STATIC_LIBS)
+        set(AVFORMAT_INCLUDE_DIRS ${PC_AVFORMAT_STATIC_INCLUDE_DIRS})
+    else()
+        set(AVFORMAT_INCLUDE_DIRS ${PC_AVFORMAT_INCLUDE_DIRS})
+    endif()
+    if (NOT AVFORMAT_INCLUDE_DIRS)
+        find_path(AVFORMAT_INCLUDE_DIRS NAMES libavformat/avformat.h)
+    endif()
+    if (NOT TARGET AVFORMAT::AVFORMAT)
+        add_library(AVFORMAT::AVFORMAT ALIAS PkgConfig::PC_AVFORMAT)
+    endif()
+else()
+    message(FATAL_ERROR "failed.")
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(AVFORMAT
+    FOUND_VAR AVFORMAT_FOUND
+    REQUIRED_VARS
+        AVFORMAT_LIBRARYS
+        AVFORMAT_INCLUDE_DIRS
+    VERSION_VAR AVFORMAT_VERSION
+)