MediaCapture: Add FFmpeg backend

CMakeModules/DuckStationDependencies.cmake

@@ -59,6 +59,16 @@ if(NOT WIN32 AND NOT APPLE)
   find_package(Libbacktrace REQUIRED)
 endif()
 
+if(NOT ANDROID AND NOT WIN32)
+  find_package(FFMPEG COMPONENTS avcodec avformat avutil swresample swscale)
+  if(NOT FFMPEG_FOUND)
+    message(WARNING "FFmpeg not found, using bundled headers.")
+  endif()
+endif()
+if(NOT ANDROID AND NOT FFMPEG_FOUND)
+  set(FFMPEG_INCLUDE_DIRS "${CMAKE_SOURCE_DIR}/dep/ffmpeg/include")
+endif()
+
 if(APPLE)
   set(CMAKE_FIND_FRAMEWORK ${FIND_FRAMEWORK_BACKUP})
 endif()