As a cross-promotion, Warner Brothers had Robin Williams and Billy Crystal make guest appearances in Friends (1994).
The concert was filmed at a park in Los Angeles. The scene took three days to film, and involved playing the same song over and over for all three days. To show the energy of the crowd, the extras had to cheer and "rock" to the music. On the first day everyone was up, yelling, jumping and punching their fists in the air, but by day three, most were too tired to even lift their arms, and many just remained seated.
Robin Williams and Billy Crystal both played mimes in previous films. Crystal in This Is Spinal Tap (1984) and Williams in Shakes The Clown (1991).
During the filming of the concert scene, Robin Williams took a break and walked into the bleachers, where he entertained the extras who gathered around him.
Before appearing in this film, Robin Williams and Billy Crystal were already a well-known comedy duo, thanks to their work on HBO's Comic Relief. The original French film, on which this is based, The ComDads (1983), also features a well-known comedy team: Pierre Richard and Gérard Depardieu. Just the previous year, Williams and Crystal had appeared (though they shared no scenes) in Hamlet (1996), which also featured Depardieu.