It's an old PBS special that aired in 2002 and it's narrated and hosted by none other than Dr. Johnny Fever himself, Howard Hesseman. The documentary features a plethora of talent, including Cousin Brucie, Scott Muni, Scott Shannon, Rick Dees, Pat St. John and of course, the father of the format, Tom Donahue.  

You can get more details about where and when this first aired here and then watch the full hour-long movie here.