Back when he pretty much invented the TV talk show, Steve Allen had a whole repertoire of recurring bits and segments, many of which have been borrowed with little modification by others who've since hosted such programs. David Letterman is the only one I can think of who has ever attempted this time-filler, which was just to point a TV camera at the street outside and have the host deliver a running silly ad-lib commentary.
I'm not sure this example of Mr. Allen doing it is entirely ad-lib. The way the video picks up interesting folks on the street, it feels to me like they taped a lot of footage and then edited it down to make sure there'd be no pauses with no one for the host to talk about. That could mean Allen's narration wasn't totally spontaneous…but maybe it was. In earlier times, he definitely did this kind of thing on his shows without pretaping or prep and it was usually very funny. I also have no idea what show this is from. The cars and the mention of Martin Mull would suggest late seventies or early eighties. If you've got a better idea, let me know…