Well, it seems original to me. OAK @ PIT, in the 1972 AFC Divisional Playoffs. A pretty impressive find if so from a time when the league was more interested in NFL Films-izing its great moments rather than presenting them in their original form.
Here the video (when there is video at all) is all pieced together from after the fact sources (you'll notice the video not matching the sound in several places, and the final score popping up even though there are still 5 seconds left), but I honestly think that the audio is taken directly from the original TV broadcast in 1972. YouTube clips tend to disappear pretty quickly, so those interested should check it out while it's hot.