Some guys offered to film a wedding but either they left the cap on or forgot to turn the camera on or something, and then tried to hide that fact from bride and groom. It could have been anniversary or birthday party.
shareIt was Cheers. Cliff bought a new camcorder and offered to videotape some family party that was happening at the bar. The battery died shortly after the event began so he and Norm just carried on pretending like everything was fine pretending to film.
It's season 11, episode 12 "Sunday Dinner". With new video camera in hand, Cliff and assistant Norm are hired by a man named Peter to videotape his parents 50th wedding anniversary to be held at cheers.