There are many ways how to produce hydrogen for cars using fuel cells. Watching the video from Toyota, it seems that cow manure is a very useful source of hydrogen.
"Fueled by Bullsh*t" is the title of the video which shows how one can produce hydrogen from the manure dropped by cows on farms. Which, in turn, is what is required for the Toyota Mirai, their first large production car driven on fuel cells. Manure is first transported to a biogas plant, where biogas is produced. Biogas gets purified into methane. Methane is, finally, under high temperature and pressure, assisted by water vapor, converted into pure hydrogen.
Toyota's video, directed by Morgan Spurlock, is their reaction to criticism directed towards cars on fuel cells. In particular, to the statement given by Tesla Motors' CEO Elon Musk, who used the word "Bullshit" a couple of years ago, when speaking about the cars using fuel cells as a method of propulsion.