Simple and small free app that can always adjust the volume and is useful for movies, music.

You can adjust the volume of music, movies, and apps, and change from advanced options to phone call and speakerphone volume.

The green button on the notification bar is the hide function.
The speaker button indicates the volume and can be muted by double-clicking in the advanced options.
If you press and hold the speaker button, you can activate the function that disappears in the advanced options.
You can resize the icon in the notification bar.