I'm listening to the repeat of (I think) last Thursday's prom*. It's Beethoven's 4th piano concerto. Ever since I first heard it it has been one of my favourite pieces of music. The soloist** is taking enormous liberties with it. I quite like what he is doing. I suspect that the cadenzas are all his own work*** as I have never heard them before, and there are some "standard" cadenzas that do the rounds which get trotted out regularly.
*It's Prom 17. Available on "Listen Again" for about a month, I think.
**Robert Levin.
***They are.