Embouchure

The embouchure is the use of facial muscles and the shaping of the lips to the mouthpiece of a wind instrument.

The proper embouchure allows the instrumentalist to play the instrument at its full range with a full, clear tone and without strain or damage to one's muscles.
While performing on a brass instrument, the sound is produced by the player buzzing his or her lips into a mouthpiece. Pitches are changed in part through altering the amount of muscular contraction in the lip formation. The performer's use of the air, tightening of cheek and jaw muscles, as well as tongue manipulation can affect how the embouchure works.

Most Professional performers, as well as instructors, use a combination called a puckered smile. It is described in "The Art of Brass Playing" and is easy to set. It is the way you blow when you cool soup, or whistle.
That is how he set the embouchure.