Film clips of musicians have been around since the 1960's, but it is generally acknowledged that Queen's Bohemian Rhapsody was the first custom-designed video to be used in their absence on Top Of The Pops.
The band were on tour, so couldn't make the recording of the show, so the video was specifically shot to use instead, and I understand that is the first time that film was shot specifically for promotional use on television which makes it the first actual pop video.