http://dangerousminds.net/comments/interstellar_zappadrive_when_frank_zappa_jammed_with_pink_floyd

From the notes of the 1969 The Amougies Tapes Zappa bootleg: Frank Zappa was present at the festival in a twofold capacity. First, as Captain Beefheart’s road manager; secondly, as M.C., assisting Pierre Lattes, a famous radio/TV presenter at the time (and the pop music editor for Actuel magazine). The latter task proved problematic given Zappa’s limited French, the prevailing language among the audience, who themselves didn’t seem to understand much English. Instead, Zappa relinquished his M.C. job for one of occasional guest guitarist. He plays with almost everybody, especially with Pink Floyd, Blossom Toes, Archie Shepp and Aynsley Dunbar, a fabulous drummer he will hire shortly thereafter. He introduces his friend Captain Beefheart and provides a powerful stimulant to all the other musicians. Most legendary, of course, is Frank Zappa’s jam with Pink Floyd on a very extended “Interstellar Overdrive”. The festival was filmed by Jerome Laperrousaz, and the film was to be called MUSIC POWER. Due to objections from various bands (most notably Pink Floyd) whose permission hadn’t been properly secured, the film was never officially released.” Simpsons creator Matt Groening asked Zappa about the festival in a 1992 interview, but oddly he doesn’t even mention sitting in with Pink Floyd: Frank Zappa: I was supposed to be MC for the first big rock festival in France, at a time when the French government was very right-wing, and they didn’t want to have large-scale rock and roll in the country. and so at the last minute, this festival was moved from France to Belgium, right across the border, into a turnip field.