It would appear that there is quite a high energy input from the clock compared to a simple pendulum. it'll either have a falling mass or a wound spring in there.
what I noticed is that the bob is going in the opposite direction after the first unwind on each side but it is being forced to reverse direction eg @ 0:55
The very visible energy conversion is KE to PE as the bob winds round the spindle and gains a little height and then PE to KE as it unwinds again and loses height, but I think the losses are great, friction of string winding around the spindles and the relatively high speed of the bob through the air causing drag losses... I'm doubtful that pendulum could complete one cycle under it's own energy.