Android – AudioManager – Controle de volume com UI nativa do sistema

Android Audio

/**
FLAG_SHOW_UI
Show a toast containing the current volume.
See also:
    adjustStreamVolume(int, int, int)
    adjustVolume(int, int)
    setStreamVolume(int, int, int)
    setRingerMode(int)
*/

https://developer.android.com/reference/android/media/AudioManager.html#FLAG_SHOW_UI