The differences between both versions are described in the order page. VideoStitch Studio Extended gives you all VideoStitch Pro features and adds the following:
Extended timeline and advanced keyframe editing:
Multi GPU processing:
Multi GPU is a unique VideoStitch feature that allows to speed up rendering by processing projects on multiple graphics cards in the same time, chose different GPU to be used by the batch stitcher and the main application, or even stitch videos while simultaneously working in third party GPU application such as traditional video editing and 3D software !