Clicking the image (in the actual interface) toggles playback.

Originally I was thinking to mimic the motion of two spindles of a cassette but the maths got a bit complex. Happy discovery was that on a touchscreen, the image becomes a jog wheel (see Videojog). Also, as a result of decoupling the circular motion from the audio timeline (to produce a smoother motion that the granularity of the timeupdate event), it gets something of the machinic nature of the tape or record player.