Is there a way to keep youtube videos etc playing even while closing the lid?

This worked before I reinstalled android with some app that I don't remember which. A common situation is that I start a youtube video, start listening and then put the phone in my pocket. And then the sound stops after closing the phone. I'd like youtube and other selected programs to keep playing. Is there a way to achieve it? I believe there was a program that could do it where a whitelisted youtube etc to keep playing in the background or similar.