The authors emphasize their ability to perform action alignment of actions performed by different people at different times. Yet it seems like with their constraining the alignment to 1D affine transformations in time (ie different frame rates or time scales) their method is unlikely to scale well to longer sequences where non-linear temporal warping becomes more pronounced. Some of this warping is apparent in the ballet clip (I'm sure there would have been more if there wasn't music being danced to), and this is a fairly short clip. I wonder how quickly performance would drop off as the linear assumptions begin to fail.