In addition to cropping the frame, it warps the image to map each frame to a set of points calculated to fit a simulated camera following a line, parabola, or a filtered version of the original camera path. When sped up, the end result is not "garbage" at all because it's a path along a perfect line/parabola.

You can 2x the video on Youtube to see for yourself. The major drawback is cropping and computation time, which is where Microsoft's technique excels.