Samsung
Use Volume Keys for Media Volume auf Samsung
On a Samsung phone, the volume keys are linked to the ringer channel by default. Pressing them while a video, song or game is running does nothing to the actual playback volume, because that level was set the last time an app controlled the media stream.
Samsung's One UI includes a switch that reassigns the physical buttons to the media channel instead. Once enabled, pressing the keys while watching a video, listening to music or playing a game adjusts that specific volume, not the ringtone.
To turn it on, go to Tap on Settings ➔ Tap on Sounds and vibration ➔ Tap on Volume ➔ Enable or disable Use Volume keys for media.
With the option enabled, the volume keys always follow whatever audio is active on screen. If no media is playing, they fall back to controlling the ringtone as usual.
This setting is useful for anyone who frequently switches between calls, notifications and media playback and wants one predictable behavior for the buttons. If separate control over notification and media volume is more important, adjusting the individual sliders in the same Volume menu is the better fix instead of relying on the physical keys.