Not sure if that fits, but maybe the piano piece is the Philip Glass album "Solo Piano", which is variation on the same base melody thorough the whole album?
It’s fewer repititions than I had remembered at a mere 840.
When John Cage, David Tudor and others gave the first public performance, it took over 18 hours and they gave a refund to audience members of 5c for each twenty minutes they stayed for
And this being HN, I feel obligated to reference a very interesting talk by Mouse Reeve about Erik Satie during a "Strange Loop" conference: