I want to make a mask on a specific area of the footage in a specific time. I drew the mask and all the frame went black,so I clicked on Mask-> invert and only the specific area I masked went black,which is exactly what I wanted.
Now I want to make it happen in a specific time, not on all timeline, but I can't find a way to do it. I thought about lowering down the mask opacity to 0% and a frame later bringing it to 100%, but if I lower down the opacity of the mask, it lowers down the opacity of the whole frame, same as
lowering down the opacity of the frame by intention, which seems weird, cause I did inverted the mask, and as I understand it, it should affect the opacity of the mask and not the whole frame...
I'm using CS4.