I use the following code to increase music volume when the user presses the VolumeUp button:

@Override
public boolean onKeyDown(int keyCode, KeyEvent e) {
    if (keyCode == KeyEvent.KEYCODE_VOLUME_UP) {
        AudioManager audio = (AudioManager)getApplicationContext().getSystemService(AUDIO_SERVICE);
        audio.adjustStreamVolume(AudioManager.STREAM_MUSIC, AudioManager.ADJUST_RAISE, AudioManager.FLAG_SHOW_UI);
        return true;
    }
}

In the Google Developer Console, I’m seeing this ANR:

This Binder call may be taking too long, causing the main thread to
wait, and triggering the ANR.

at android.os.BinderProxy.transactNative (Native method)
at android.os.BinderProxy.transact (Binder.iava: 1154)
at android.media.IAudioServiceSStub$Proxy.adjustStreamVolume (IAudioService.java: 1150)
at android.media.AudioManager.adjustStreamVolume (AudioManager.java: 820)
at com.example.MyActivity.onKeyDown (MyActivity.java:42)

Your app’s code results in the Binder call above. Code that triggers
Binder calls should be moved out of the main thread.

Should calls to AudioManager.adjustStreamVolume be performed on a background Thread?

@Override
public boolean onKeyDown(int keyCode, KeyEvent e) {
    if (keyCode ==  KeyEvent.KEYCODE_VOLUME_UP) {
        new Thread(this::increaseVolume).start();
        return true;
    }
}

private void increaseVolume() {
    AudioManager audio = (AudioManager)getApplicationContext().getSystemService(AUDIO_SERVICE);
    audio.adjustStreamVolume(AudioManager.STREAM_MUSIC, AudioManager.ADJUST_RAISE, AudioManager.FLAG_SHOW_UI);
}