android支持网络流的视频播放器，无法播放

[xihao6334]

做一个支持网络流的视频播放器，遇到视频无法播放的难题，请教各路大神，代码如下：

public class MainActivity extends Activity {
private String videoUri = null;
private VideoView videoView = null;
Button bt_confirm = null;
private EditText et_mrl = null;
//Button bt_cancel;
//private AlertDialog dialog;

@Override
protected void onCreate(Bundle savedInstanceState) {
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
videoView = (VideoView)findViewById(R.id.video_view);
et_mrl = (EditText)findViewById(R.id.et_mrl);
final ImageButton ib_play = (ImageButton)findViewById(R.id.ib_play);
bt_confirm = (Button)findViewById(R.id.bt_confirm);
//bt_cancel = (Button)findViewById(R.id.bt_cancel);


// final Uri uri = Uri.parse(videoUri);
bt_confirm.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
videoUri=et_mrl.getText().toString();
playRtspStream(videoUri);
}
});
}
//play rtsp stream  
private void playRtspStream(String Url) {
Toast.makeText(MainActivity.this,Url+"!!!",Toast.LENGTH_SHORT).show();
Uri uri = Uri.parse(Url);
videoView.setVideoURI(uri);
videoView.requestFocus();
videoView.start();
}
}