I haven't watched through the whole thing, but the C code I saw from skipping through looks like it's actually the output from CWEB [1], one of Knuth's literate programming tools. It combines C source code with long-form documentation, and it can either be preprocessed to TeX (to give that nice, pretty printed document that Knuth shows in the video) or to standard C source code to compile and run.
CWEB is one of Knuth's languages of choice, and he's got tons of code written in it on his website [2], including versions of some of the stuff he's demoing on-screen.
CWEB is one of Knuth's languages of choice, and he's got tons of code written in it on his website [2], including versions of some of the stuff he's demoing on-screen.
[1] http://www-cs-faculty.stanford.edu/~uno/cweb.html
[2] http://www-cs-faculty.stanford.edu/~uno/programs.html