@igorbeg thanks! I took a look at the linked video & will look at more…
Because I have image sequences and it is recommended to keep them at 1:1, I will see if I can remove the background in Natron then render the images as as a video file. So I can import & proxy all video scaled to 1:4. BTW can cinelerra mask with some sort of edge detection by any chance? I have not used a green screen behind my subject and the background and subject have some overlapping hues and exposure so chromakey is not a good option. Otherwise I would have to change the mask almost on every frame…