we are experiencing some problems with the Mastermath Vimeo account. Some of the recently uploaded lectures do not play back properly (slow-motion, without sound synchronization). We are working (with Vimeo) on resolving this as soon as possible.
In the meanwhile, if you experience problems you can download the original video file (use the 'download' button under the video, and select the 'original' format). These should play back properly on your own device.