On the last command line argument that you've sent, (-y -f rawvideo -pix_fmt rgb24 -s %WIDTH%x%HEIGHT% -r %FPS% -i - %FILTERS%-an -c:v libx265 -preset ultrafast -pix_fmt yuv420p "%FILENAME%" ), the file size become 12 MB. It changed a lot, but it is too long. ><
Anyway, thank you ma'am for helping me out. :)