

By duping the clip to a second layer and masking around a clean part of the frame you can then reposition the masked clip to cover the unwanted part of the bottom layer. I use this often when I have a client in the room during a finishing session and we notice a little something in the frame that needs to be removed. This little trick is fast and also means you can use tracking as well.
MASKING IN PREMIERE PRO FREE
In the Effect Controls click on the type of mask you'd like: ellipse, polygon, or free draw.Add a mask to the adjustment layer using the process described above. Drag this to the sequence and position it above the clips you wish to effect.

A new layer will be automatically added to the Project browser. The clip you are masking is now invisible. In the Project browser go to New Item > Adjustment Layer. It can help to change the Zoom level so you can see the space outside your frame.
MASKING IN PREMIERE PRO PRO
These are quite frankly awesome and I already do not like to think about using Premiere Pro without them. The CC 2014.1 release blessed us with a free-draw polygon pen tool and adjustable on-screen Bezier adjustments. It is an incredibly useful feature, but one whose boundaries were quickly found. Easily one of the most anticipated and discussed features in Premiere Pro CC 2014 has been Masking and Tracking Effects.
