BSPlayer free, android app, allows to increase and decrease the speed of the video or audio you are listening to.
In order to do that, click on the “speedometer” icon (see red arrow), and select the execution speed (e.g. 90 %, 110%)
Music (any audio file) can be listened to with the screen turned off.
You can vertically drag the finger on the screen to adjust brightness (left) or volume (right), and horizontally to go back / forward.
I found this app very useful to listen to “youtube watch later” video I’ve previously downloaded.