audioManager = (AudioManager) activity.getSystemService(Context.AUDIO_SERVICE);//获取音频管理器
videoMaxVolume = audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);//获取最大音量

volume = audioManager.getStreamVolume(AudioManager.STREAM_MUSIC);//获取当前音量

// 变更声音
audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, index, 0);

一段滑动改变音量的代码

private void onVolumeSlide(float percent) {
        if (volume == -1) {
            volume = audioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
            if (volume < 0)
                volume = 0;
        }
        hide(true);

        int index = (int) (percent * videoMaxVolume) + volume;
        if (index > videoMaxVolume)
            index = videoMaxVolume;
        else if (index < 0)
            index = 0;
        // 变更声音
        audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, index, 0);
        // 变更进度条
        int i = (int) (index * 1.0 / videoMaxVolume * 100);
        String s = i + "%";
        // 显示
        $.id(R.id.video_img_tip).image(R.mipmap.volume_up);
        $.id(R.id.ll_volume_brightness_tip).visible();
        $.id(R.id.video_tv_tip).text(s).visible();
    }