It is a Sonatina from JS Bach's Cantata 106
For me this is sublime: perfection in a short (two and a half minutes), small group, instrumental piece.
I love it for its use of my (secret) favourite instrument - the treble recorder: indeed a pair of them.
What makes this unique in my experience is two features: the loveliness of the melody; and the effect which Bach appears to have invented just for this - of using one recorder to hold a note while the other oscillates between that same note and others below or above it.
The above YouTube recording is inferior to the one I first heard - which was a 1970s LP featuring David Munrow, with the Early Music Consort of London - I recorded it 'live' onto a cassette tape which I long treasured....