Amanda Seyfried sang Gimme! Gimme! Gimme! (A Man After Midnight) with Dominic Cooper behind the mixing desk.  In between shots of them both in the studio, and Amanda in New York, were shots fromt the forthcoming film, Mamma Mia! The Movie.

Benny appears in the final few seconds to take control!

I am not entirely sure what the details are about this clip - what was its purpose?  Presumably it was part of drip-feeding information and clips from the film to build the anticipation for the film's release.

There were at least two versions of the video. The version included as a bonus feature on the Mamma Mia! The Movie DVD uses the correct mix, but the video in this entry appears to be the TV version, which uses a “PAL speed” mix (4% faster with a 0.7 semitone increase).

Thanks to Julian Körner and Aaron Evans.
YouTube link c/o Decca Records US