It's the first movement of Brandenburg Concerto No. 2 by J. S. Bach for violin, Blockflöte, (recorder) trumpet and oboe. Here's how the instrumentation stands in the video:
Concertino:(If you're not sure what a melodica is, look them up on Wikipedia, there's a good page of info there.)
Trumpet: Soprano melodica
Alto recorder: Alto recorder
Oboe: Alto melodica
Violin: Alto melodica
Ripieno:
Vln 1, Vln 2, Vla: Alto melodica
Cello and Bass: Bass melodica
"... The winds are now exalted in the Concerto No. 2 in F Major. The solo group is made up of violin, recorder, oboe and trumpet. This is not just an unusual combination, it is unprecedented. Far from tailoring the writing to suit the disparate bunch, Bach treats them virtually as equals. If counterpoint is akin to musical juggling, here the composer is juggling eggs along with a basketball and a running chainsaw. The work is in fact, a bold attempt at a hitherto unknown musical democracy."
-From the liner notes of the 2000 recording by Apollo's Fire.