Obviously, this question concerns only composers who could have been recorded after 1877, the start of the poor, impractical Acoustic Age of recording equipment; or more realistically, 1925, the Electric Age with improved recording.
I am interested in hearing conductors' participation or playing in their own music (e.g. composers playing their own Piano Concertos as the soloist, or conducting their own orchestral works); but it is too inefficient to Google or search on Youtube for such recordings for each.