Android开发中，要想使用MediaPlayer构建一个音频合并的工具，可以通过以下步骤进行实现：

1. 创建多个MediaPlayer对象。
2. 为每个MediaPlayer对象设置不同的音频源。
3. 准备每个MediaPlayer对象来播放音频。
4. 将每个MediaPlayer对象的音频输出通道合并到一个混音器上。
5. 将混音器输出连接到AudioTrack播放。

实现的示例代码如下：

import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioTrack;
import android.media.MediaPlayer;
import android.media.audiofx.Visualizer;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import java.io.IOException;

public class MainActivity extends AppCompatActivity implements MediaPlayer.OnPreparedListener {

  private MediaPlayer mMediaPlayer1, mMediaPlayer2;
  private boolean mIsMediaPlayer1Prepared = false, mIsMediaPlayer2Prepared = false;
  private boolean mIsPlayingAudio = false;

  private Visualizer mVisualizer;
  private AudioTrack mTrack;

  private int mSamplingRate;
  private int mBufferSize;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mSamplingRate = AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_SYSTEM);
    mBufferSize = AudioTrack.getMinBufferSize(mSamplingRate, AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_16BIT);

    mTrack = new AudioTrack(AudioManager.STREAM_MUSIC, mSamplingRate, AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_16BIT, mBufferSize, AudioTrack.MODE_STREAM);

    mMediaPlayer1 = new MediaPlayer();
    mMediaPlayer1.setDataSource("http://soundbible.com/grab.php?id=1066&type=wav");
    mMediaPlayer1.setOnPreparedListener(this);
    mMediaPlayer1.prepareAsync();

    mMediaPlayer2 = new MediaPlayer();
    mMediaPlayer2.setDataSource("http://soundbible.com/grab.php?id=29&type=wav");
    mMediaPlayer2.setOnPre