In the video, Andrew creates music live on his laptop by writing a few lines of Scheme.

Besides the musical aspects, the video also provides an example of changing snippets code on the fly. The snippets can be started while the rest of the program continues to run. That's based on Extempore and the Impromptu language that they created specifically for cyber-physical computing (https://en.wikipedia.org/wiki/Impromptu_%28programming_envir...)