Android : How to set MediaPlayer volume programmatically?

Using AudioManager, you can simply control the volume of media players.

AudioManager audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, 20, 0);

also from MediaPlayer (But I didn’t try that)

setVolume(float leftVolume, float rightVolume)

Since: API Level 1

Sets the volume on this player. This API is recommended for balancing
the output of audio streams within an application. Unless you are
writing an application to control user settings, this API should be
used in preference to setStreamVolume(int, int, int) which sets the
volume of ALL streams of a particular type. Note that the passed
volume values are raw scalars. UI controls should be scaled
logarithmically.

Parameters

leftVolume left volume scalar

rightVolume right volume scalar

Hope this help

    audio = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

For Volume UP

 audio.adjustStreamVolume(AudioManager.STREAM_MUSIC,
                        AudioManager.ADJUST_RAISE, AudioManager.FLAG_SHOW_UI);

for Volume Down

audio.adjustStreamVolume(AudioManager.STREAM_MUSIC,
                        AudioManager.ADJUST_LOWER, AudioManager.FLAG_SHOW_UI);

You do have the setVolume method in the MediaPlayer class. See here