Hey Kev48us,
I'm a big music fan, so I'm always watching the latest music videos on YouTube and I want you to be able to do the same. To utilize the YouTube application you need to keep the screen on the YouTube application. If the screen shuts off the sound will stop playing. This is how the YouTube application was designed. I would recommend submitting feedback to the developer through the Google Play store to see if that can be changed.
NicholasB_VZW
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