Hi all,
I'm working on a time-lapse project where I have taken 240 shots of a highway heading into my city, and have erased the cars from the shot, creating the look of an "empty city". This will be one of many sequences like this.
I got the highway background plate perfect, no cars, and I threw that into my AE comp (CS6), along with the 240 images as a JPEG sequence. I've layered the background plate on top of the image sequence and used a mask to "hide" the cars from the highway.
The problem is, some of the cars are taller than the roadway (trucks, busses, etc), so they push into the upper part of the frame where the motion is supposed to happen. If I extend the mask upward, you can see a literal bisection between the still plate and the animated JPEGs. If I just move the mask path to hide cars as they go by, the moving mask becomes VERY obvious in the exported QuickTime.
I've attached a still of my setup and a short video for explanation. If anyone can help me salvage this shot, I'd be very grateful. I do NOT want to have to erase out the tops of the cars in every photo I took 
