This is Wolfgang Amadeus Mozart's "Serenade Nº 10 for winds in B flat major, "Gran Partita," its third movement, "Adagio."
Performed by the Orchestre des Champs-Élysées, conducted by Philippe Herreweghe.
In Miloš Forman's superb movie "Amadeus," here's how Antonio Salieri describes this music:
"On the page, it looked... nothing!
The beginning simple, almost comic.
Just a pulse: bassoons, basset horns, like a rusty squeezebox!
And then, suddenly, high above it, an oboe!
A single note, hanging there, unwavering, until a clarinet took it over, sweetened it into a phrase of such delight!
This was no composition by a performing monkey!
Yes, it was music I had never heard.
Filled with such longing, such unfulfilled belonging!
It seemed to me I was hearing the voice of God!"
What more could one say?
Please consider supporting my work (VERY MUCH in need of support these days). You can make donations via PayPal, starting from here : vudici.net/movies/morphing.html#new123108 (this type of work receives very little help, if any, from the usual channels).