In this fascinating clip, we can see and hear how Mr Evans and bassist Eddie Gomez work out their "improvisation" for the TV director. We can see how musicking is happening. I so appreciate this documentation of a rehearsal because it dispels the idea that jazz is just made up on the spot. There is certainly freedom of interpretation in jazz and Mr Evans, trained as a composer, took liberties in a performance. BUT there is so much that is planned and rehearsed prior to performance.
And Bill Evans' music is inspired and continues to influence musicians in all genres to this very day. Love this music.