Samsung SM-G930W8 User Manual Addendum page 14

Basics
If the screen is locked, you must unlock it to view notifications.
Controlling music playback when the screen is off
You can control music playback when the screen is off, without turning on the screen.
Double-tap the title of the currently playing song with your finger. The music controller will
appear. Double-tap the icons to control the playback.
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