Are these songs played by a pianist or computer generated?
All of the songs on PianoTrax are played by professional pianist, Thomas Griep. He has conducted and played for many artists including: Carol Channing, Nathan Lane, Rita Moreno, Tommy Tune, Melissa Manchester, Loretta Devine, Olivia Newton-John, Kate Shindle, Lea Salonga, Lindsey Mendez, Leslie Odom Jr., and Sutton Foster.
It requires a lot of experience for the accompanist to know if the sheet music should be played exactly as written or leave out the doubled melody in the accompaniment so the singer has some vocal freedom.
Most of the tracks on the site have a "melody" version to help you learn the song and a "piano" version to perform with.