public void setStereoVolume(float leftGain, float rightGain) {
        mVolumeLeft = leftGain;
        mVolumeRight = rightGain;

        if(mAudioTrack != null) {
            mAudioTrack.setStereoVolume(leftGain, rightGain);
        }
    }
@see android.media.AudioTrack#setStereoVolume(float, float)
@deprecated deprecated in API21, prefer use of {@link #setVolume(float)}
MediaPlayer/src/main/java/net/protyposis/android/mediaplayer/AudioPlayback.java