Removing black bars from captured video

[darind]

When using RecordRTC in a chrome extension to capture the active tab, the resulting video is scaled and some black bars appear on top and bottom (letterboxed). Is it possible to control this behaviour with the API in order to remove those bars or at least be able to calculate their exact size?

The reason I need to know their size is because I perform some transformations on the video frames and I have to draw some shapes on specific position relative to the screen origin point (0x0).