macOS how can I capture the desktop screen and save it to a bmp file

Hi all,

I ever used
system("screencapture ./xx.bmp");
in my program.

It works but will freeze the screen a little bit.
Actually I want to capture the screen every 1 second.
So if a video is playing, the capture function causes the video not playing smoothly.
Any suggestions?

Thanks a lot for your reply!!