Youtube has an option to change the playback speed of videos that speeds up or slows down a video's audio without affecting its pitch. I know that there are a number of different algorithms that can do this, but I am curious as to which specific algorithm Youtube uses because it seems to work rather well.
Also, are there any open source libraries implementing this algorithm?
I found this article on the subject dating back to 2017, I presume it's still valid or should give you some pointers: https://www.googblogs.com/variable-speed-playback-on-mobile/
It reads, in part:
"On Android, we used the Sonic library for our audio manipulation in ExoPlayer. Sonic uses PICOLA, a time domain based algorithm. On iOS, AVplayer has a built in playback rate feature with configurable time stretching."