YouTube isn’t just for home video and TV shows. There’s lots of arts footage, too. “Seeing these artists, most of whom are now known to us only through their recordings, is an awe-inspiring experience. To watch Art Tatum rippling through a bristlingly virtuosic version of Jerome Kern’s “Yesterdays,” or Richard Strauss conducting his tone poem “Till Eulenspiegel” with a cool detachment that borders on the blasé, is to learn something about the essence of their art that no verbal description, however insightful or evocative, can supply.”