Size Settings
Click "GIF Options" toolbar button, then select "Size" tab page.
"Crop" group:
Crop the source video: Check this box to crop the source video when
converting, this enable you to convert certain region of the video instead of
it's full screen.
Left: X value of the top-left corner of the crop region.
Width: Width of the crop region.
Top: Y value of the top-left corner of the crop region.
Height: Height of the crop region.
See Also
General Settings