寫一個很平常的音樂播放方法，發現聲音很小，於是呼叫MediaPlayer.setVolume來設定聲音，結果無效，程式碼如下：

 private static MediaPlayer m = null;

    public void play(Context context) {

        m = new MediaPlayer();
        m = MediaPlayer.create(context, R.raw.myMusic);
        m.setAudioStreamType(AudioManager.STREAM_MUSIC);
        m.setVolume(1
 
f, 1f);
        m.start();        

        m.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer arg0) {
                m.release();
                Log.d("MediaPlayer:", "release");
            }
        });

查詢到的解決方法是將setVolume方法放到play之後，如下：

        m = new MediaPlayer();
        m = MediaPlayer.create(context, R.raw.myMusic);
        m.setAudioStreamType(AudioManager.STREAM_MUSIC);
          m.start(); 
        m.setVolume(1f, 1f);

再次測試發現聲音已經變大，問題解決

檢視setVolume原始碼的註釋：
public void setVolume(float leftVolume, float rightVolume)

/**
     * 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
     * {@link AudioManager#setStreamVolume(int, int, int)} which sets the volume of ALL streams of
     * a particular type. Note that the passed volume values are raw scalars in range 0.0 to 1.0.
     * UI controls should be scaled logarithmically.
     *
     * @param leftVolume left volume scalar
     * @param rightVolume right volume scalar
     */

其中的兩個引數分別是左右聲道聲音大小，取值範圍為0~1