android之VideoView和视频播放View的扩展
1.概念及扩展
VideoView 是android 系统提供的一个媒体播放显示和控制的控件。其结构层次如下：
原型：VideoView extends SurfaceView implements MediaController.MediaPlayerControl
类结构：
java.lang.Object
↳ android.view.View
↳ android.view.SurfaceView
↳ android.widget.VideoView
通过VideoView 的原型可知：如果构建更为复杂和有特色个性的视频View，需要继承SurfaceView 和实现MediaPlayerControl接口。其中SurfaceView 为显示提供支持，MediaPlayerControl则为媒体控制提供了支持。
2.案例
1)VideoView案例
(我们没有管理MediaPalyer的各种状态，这些状态都让VideoView给封装了，并且，当VideoView创建的时候，MediaPalyer对象将会创建，当VideoView对象销毁的时候，MediaPlayer对象将会释放。)
布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<VideoView android:id="@+id/video_view" android:layout_width="match_parent" android:layout_height="match_parent"
android:layout_centerInParent="true" />
</LinearLayout>
主程序：
public class VideoPlayer extends Activity implements MediaPlayer.OnErrorListener, MediaPlayer.OnCompletionListener {
public static final String TAG = "VideoPlayer";
private VideoView mVideoView;
private Uri mUri;
private int mPositionWhenPaused = -1;
private MediaController mMediaController;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//Set the screen to landscape.
this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
mVideoView = (VideoView)findViewById(R.id.video_view);
//Video file
mUri = Uri.parse(Environment.getExternalStorageDirectory() + "/1.3gp");
//Create media controller，组件可以控制视频的播放，暂停，回复，seek等操作，不需要你实现
mMediaController = new MediaController(this);
mVideoView.setMediaController(mMediaController);
}
public void onStart() {
// Play Video
mVideoView.setVideoURI(mUri);
mVideoView.start();
super.onStart();
}
public void onPause() {
// Stop video when the activity is pause.
mPositionWhenPaused = mVideoView.getCurrentPosition();
mVideoView.stopPlayback();
super.onPause();
}
public void onResume() {
// Resume video player
if(mPositionWhenPaused >= 0) {
mVideoView.seekTo(mPositionWhenPaused);
mPositionWhenPaused = -1;
}
super.onResume();
}
public boolean onError(MediaPlayer player, int arg1, int arg2) {
return false;
}
public void onCompletion(MediaPlayer mp) {
this.finish();
}
}
2)自定义VideoView
和VideoView实现类似，继承了SurfaceView并且实现了MediaPlayerControl。
public class CustomerVideoView extends SurfaceView implements
MediaPlayerControl {
private static String TAG = "customer.videoplayer";
private boolean pause;
private boolean seekBackward;
private boolean seekForward;
private Uri videoUri;
private MediaPlayer mediaPlayer;
private Context context;
private OnPreparedListener onPreparedListener;
private int videoWidth;
private int videoHeight;
private MediaController mediaController;
protected SurfaceHolder surfaceHolder;
private Callback surfaceHolderCallback = new SurfaceHolder.Callback() {
public void surfaceChanged(SurfaceHolder holder, int format, int w,
int h) {
}
public void surfaceCreated(SurfaceHolder holder) {
surfaceHolder = holder;
if (mediaPlayer != null) {
mediaPlayer.setDisplay(surfaceHolder);
resume();
} else {
openVideo();
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
surfaceHolder = null;
if (mediaController != null) {
mediaController.hide();
}
release(true);
}
};
private void release(boolean cleartargetstate) {
if (mediaPlayer != null) {
mediaPlayer.reset();
mediaPlayer.release();
mediaPlayer = null;
}
}
public void resume() {
if (surfaceHolder == null) {
return;
}
if (mediaPlayer != null) {
return;
}
openVideo();
}
public CustomerVideoView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
this.context = context;
this.initVideoView();
}
public CustomerVideoView(Context context, AttributeSet attrs) {
super(context, attrs);
this.context = context;
this.initVideoView();
}
public CustomerVideoView(Context context) {
super(context);
this.context = context;
this.initVideoView();
}
@Override
public boolean canPause() {
return this.pause;
}
@Override
public boolean canSeekBackward() {
return this.seekBackward;
}
@Override
public boolean canSeekForward() {
return this.seekForward;
}
@Override
public int getBufferPercentage() {
return 0;
}
@Override
public int getCurrentPosition() {
return mediaPlayer!=null?mediaPlayer.getCurrentPosition():0;
}
@Override
public int getDuration() {
return mediaPlayer!=null?mediaPlayer.getDuration():0;
}
@Override
public boolean isPlaying() {
return false;
}
@Override
public void pause() {
}
@Override
public void seekTo(int mSec) {
}
@Override
public void start() {
}
public void setVideoURI(Uri uri) {
this.videoUri = uri;
openVideo();
requestLayout();
invalidate();
}
private void openVideo() {
this.mediaPlayer = new MediaPlayer();
try {
this.mediaPlayer.setDataSource(this.context, this.videoUri);
} catch (Exception e) {
Log.e(TAG, e.getMessage());
throw new RuntimeException(e);
}
this.mediaPlayer.prepareAsync();
this.mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
this.mediaPlayer.setOnPreparedListener(onPreparedListener);
attachMediaController();
}
private void attachMediaController() {
if (mediaPlayer != null && mediaController != null) {
mediaController.setMediaPlayer(this);
View anchorView = this.getParent() instanceof View ? (View) this
.getParent() : this;
mediaController.setAnchorView(anchorView);
mediaController.setEnabled(true);
}
}
public void setMediaController(MediaController controller) {
if (mediaController != null) {
mediaController.hide();
}
mediaController = controller;
attachMediaController();
}
public void setOnPreparedListener(OnPreparedListener onPreparedListener) {
this.onPreparedListener = onPreparedListener;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int width = getDefaultSize(videoWidth, widthMeasureSpec);
int height = getDefaultSize(videoHeight, heightMeasureSpec);
if (videoWidth > 0 && videoHeight > 0) {
if (videoWidth * height > width * videoHeight) {
height = width * videoHeight / videoWidth;
} else if (videoWidth * height < width * videoHeight) {
width = height * videoWidth / videoHeight;
}
}
Log.i(TAG, "setting size: " + width + ‘x’ + height);
setMeasuredDimension(width, height);
}
private void initVideoView() {
videoWidth = 0;
videoHeight = 0;
getHolder().addCallback(surfaceHolderCallback);
getHolder().setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
setFocusable(true);
setFocusableInTouchMode(true);
requestFocus();
}
}
一般情况下，android界面的绘制和更新，要交给主ui线程来操作，通过Handler机制。但是播放视频，需要比较优先和实时的改变和绘制界面。android提供了使用单独线程绘制UI的机制，就是SurfaceView。使用SurfaceView，需要实现SurfaceHolder.Callback接口：
- surfaceCreated，在Surface（SurfaceView内部包含一个Surface实例）创建后，会立即调用该方法，可在该方法中做绘制界面相关的初始化工作；
- surfaceChanged，当Surface的状态发生变化，比如大小，会调用该方法，在surfaceCreated方法调用过至少会调用一次该方法；
- surfaceDestroyed，当销毁Surface的时候调用。
开发者不能直接操作Surface实例，要通过SurfaceHandler，在SurfaceView中可以通过getHandler方法获取到SurfaceHandler实例。
SurfaceHander有一些类型，用来标识Surface实例界面数据来源，可以通过setType来操作：
- SURFACE_TYPE_NORMAL：RAM缓存的原生数据
- SURFACE_TYPE_HARDWARE：通过DMA，direct memory access，就是直接写屏技术获取到的数据，或者其他硬件加速的数据
- SURFACE_TYPE_GPU：通过GPU加速的数据
- SURFACE_TYPE_PUSH_BUFFERS：标识数据来源于其他对象，比如照相机，比如视频播放服务器（android内部有视频播放的服务器，所有播放视频相当于客户端）
CustomerVideoView的构造方法，使用超类的构造方法。都会执行initVideoView()方法用来初始化界面和参数。另外一个主要的内容是openVideo()方法：
- mediaPlayer.prepareAsync()，用来异步准备播放，另外还有个prepare()方法，是同步的，也就是全部下载完毕才能播放，显然，在播放网上视频的时候需要用前者；
- 通过attachMediaController()方法，把控制条附加到播放视频的SurfaceView上，这里实现的不完全，因此还不能使 用，仅仅是把MediaPlayerControl实例通过setMediaPlayer方法设置一下，供OnPreparedListener用来得到 加载成功的回调，另外供外面代码调用得到视频的时长和当前时长。
