Apply Selector To 1 Section Only

I need to select a black section in the middle of a video frame. If I use the select tool, it also selects black section on other parts of the frame, no matter how long I play with variables. Can I use the selection tool only on 1 area of the frame, and not selecting the black parts in the other sections? Using masks maybe?
Thanks.

There are many ways to affect areas of a frame, rather than the entire image. Those methods are well covered in the training books BMD has made available to us.

https://www.blackmagicdesign.com/produc ... e/training

There are many ways to affect areas of a frame, rather than the entire image. Those methods are well covered in the training books BMD has made available to us.

https://www.blackmagicdesign.com/produc ... e/training

Thanks. Super helpful.