plugins: Suppress warnings about implicit integer downcasts

Returned values are usually 64-bit in length but commonly stored in
16-bit integers anyway.

plugins/obs-ffmpeg/CMakeLists.txt

@@ -45,6 +45,7 @@ target_sources(
           obs-ffmpeg-video-encoders.c
           obs-ffmpeg.c)
 
+target_compile_options(obs-ffmpeg PRIVATE $<$<COMPILE_LANG_AND_ID:C,AppleClang,Clang>:-Wno-shorten-64-to-32>)
 target_compile_definitions(obs-ffmpeg PRIVATE $<$<BOOL:${ENABLE_FFMPEG_LOGGING}>:ENABLE_FFMPEG_LOGGING>)
 
 target_link_libraries(