It's a bundle of baling wire. Those flat blocks lying at an angle just to the left of the hopper have grooves in them. They go between each section that will be a bale and the wire is fed from one side through the groove to the other side then along the bale and back to the beginning side through the groove on the block at the other end of the bale. The wire is pulled back to the the end of the wire that has a pre-made loop in it and tied off. One wire part way down from the top and a second wire part way up from the bottom. As the bales are pushed out of the end, the blocks fall away since the wire only went through a groove. The block then is reused for more bales.

Seems like it'd have to be pulleys, or a transmission of some sort !