MediaPlayer只有声音没图象，

package com.gushi;import java.io.IOException;import android.app.Activity;import android.media.AudioManager;import android.media.MediaPlayer;import android.os.Bundle;import android.view.SurfaceHolder;import android.view.SurfaceView;     public class app_2 extends Activity {    private MediaPlayer mp =new MediaPlayer();    private SurfaceHolder surfaceHolder;    private SurfaceView surfaceView;      public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.app2);                        surfaceView = (SurfaceView) findViewById(R.id.SurfaceView02);        surfaceHolder = surfaceView.getHolder();        surfaceHolder.setFixedSize(100, 100);        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);                         mp.reset();//恢复到未初始化的状态           mp=MediaPlayer.create(app_2.this, R.raw.b);//读取视频           mp.setAudioStreamType(AudioManager.STREAM_MUSIC);           mp.setDisplay(surfaceHolder);//设置屏幕                      try {               mp.prepare();                          } catch (IllegalArgumentException e) {               // TODO Auto-generated catch block               e.printStackTrace();           } catch (IllegalStateException e) {               // TODO Auto-generated catch block               e.printStackTrace();           } catch (IOException e) {               // TODO Auto-generated catch block               e.printStackTrace();           }           mp.start();              }                }