一起学Android之音频视频

概述

Android多媒体框架支持各种常见的媒体类型，可以很容易地将音频、视频和图像集成到App中。通过MediaPlayer Api，可以从应用程序资源（RAW）、文件系统或网络上数据流资源来播放音频或视频。本文演示了如何通过Api播放音频和视频文件，来获得良好性能和愉快的用户体验，仅供学习分享使用，如有不足之处，还请指正。

涉及知识点

1. MediaPlayer 可以用来控制audio/video文件或流播放的类。通过此类，可以方便的控制音频/视频文件的播放，暂停和停止等操作。
2. Uri 统一资源标识符(Uniform Resource Identifier，或URI)是一个用于标识某一互联网资源名称的字符串。
3. VideoView 自带的一种播放视频的组件。
4. SurfaceView 可以通过后台绘制显示的视图组件。

Activity中播放音频

页面上播放音频文件，步骤如下：

1. 准备资源文件，并播放

 private MediaPlayer mMediaPlayer;

     /**
      * 开始
      * @param v
      */
     public void bn_start(View v){
         if(mMediaPlayer==null) {
             ready();
         }
         mMediaPlayer.start();
     }

  /**
      * 创建MediaPlayer并到prepare状态
      */
     private void ready(){
         if(mMediaPlayer==null){
             mMediaPlayer=new MediaPlayer();//Idle
             //Log.i("TAG", "ready: "+filePath);
             File file=new File(Environment.getExternalStorageDirectory(),"goldfallen.mp3");
             Log.i("TAG", "ready: "+file.getPath());
             Log.i("TAG", "ready: "+file.exists());
             Uri uri= Uri.fromFile(file);
             try {
                 mMediaPlayer.setDataSource(AudioActivity.this,uri);
                 mMediaPlayer.prepare();//Prepared
             } catch (IOException e) {
                 Log.i("TAG", "ready: "+ e.getMessage());
                 e.printStackTrace();
             }
         }
     }

2. 暂停播放

 /**
      * 暂停
      * @param v
      */
     public void bn_pause(View v){
         if(mMediaPlayer!=null && mMediaPlayer.isPlaying()){
             mMediaPlayer.pause();
         }
     }

3. 停止

   /**
      * 停止
      * @param v
      */
     public void bn_stop(View v){
         if(mMediaPlayer!=null && mMediaPlayer.isPlaying()){
             mMediaPlayer.stop();
             mMediaPlayer.release();
             mMediaPlayer=null;
         }
     }

4. 释放资源（当页面销毁时，播放资源也要同时释放）

  @Override
     protected void onDestroy() {
         if(mMediaPlayer!=null && mMediaPlayer.isPlaying()){
             mMediaPlayer.stop();
             mMediaPlayer.release();
             mMediaPlayer=null;
         }
         super.onDestroy();
     }

5. 通过静态函数创建对象

 /**
      * D:\Android\Project\DemoMedia\app\src\main\res\raw\A2012.mp3:
      * Error: 'A' is not a valid file-based resource name character:
      * File-based resource names must contain only lowercase a-z, 0-9, or underscore
      */
     private void ready2(){
         if(mMediaPlayer==null){
             mMediaPlayer= MediaPlayer.create(this,R.raw.ab2012);
         }
     }

通过服务来播放音频

当页面关闭时，音频文件还可以在后台播放。步骤如下：

1. 定义后台服务，当服务启动时，创建MediaPlayer对象，并注册服务接收对象。

 public class AudioService extends Service {

     private MediaPlayer mMediaPlayer;

     private OperatorReceiver mReceiver;

     public AudioService() {
     }

     @Override
     public void onCreate() {
         super.onCreate();
         mMediaPlayer=new MediaPlayer();
         mReceiver=new OperatorReceiver();
         IntentFilter filter=new IntentFilter("operator.receiver");
         registerReceiver(mReceiver,filter);
     }

     @Override
     public IBinder onBind(Intent intent) {
         return null;
     }

     @Override
     public int onStartCommand(Intent intent, int flags, int startId) {
         Log.i("TAG", "onStartCommand: ----ready ");
         ready();
         return super.onStartCommand(intent, flags, startId);
     }

     @Override
     public void onDestroy() {
         if(mMediaPlayer!=null && mMediaPlayer.isPlaying()){
             mMediaPlayer.stop();
         }
         if(mMediaPlayer!=null){
             mMediaPlayer.release();
             mMediaPlayer=null;
         }
         unregisterReceiver(mReceiver);
         super.onDestroy();
     }

     private void start(){
         mMediaPlayer.start();
     }

     private  void pause(){
         mMediaPlayer.pause();
     }

     private void stop(){
         mMediaPlayer.stop();
         ready();
     }

     private void ready(){
         mMediaPlayer.reset();
         try {
             String filePath= Environment.getExternalStorageDirectory()+"/ab2012.mp3";
             Log.i("TAG", "ready: "+filePath);
             File file=new File(filePath);
             if(file.exists()) {
                 mMediaPlayer.setDataSource(filePath);
                 mMediaPlayer.prepare();
             }else{
                 Log.i("TAG", "ready: 文件不存在 ");
             }
         } catch (IOException e) {
             Log.i("TAG", "ready: "+e.getMessage());
             e.printStackTrace();
         }
     }
 }

2. 操作接收者定义如下：

  /**
      * 操作接收器
      */
     class OperatorReceiver extends BroadcastReceiver
     {
         @Override
         public void onReceive(Context context, Intent intent) {
             int cmd=intent.getIntExtra("cmd",-1);
             Log.i("TAG", "onReceive: "+cmd);
             switch (cmd){
                 case Tools.PLAY:
                     start();
                     break;
                 case Tools.PAUSE:
                     pause();
                     break;
                 case Tools.STOP:
                     stop();
                     break;
                 default:
                     start();
                     break;

             }
         }
     }

3. 启动服务

   Intent intent =new Intent(this,AudioService.class);
   startService(intent);

4. 前台Activity通过发送广播命令进行控制音频的播放与暂停

 /**
      * 开始
      * @param v
      */
     public void bn_start(View v){
         Intent intent=new Intent("operator.receiver");
         intent.putExtra("cmd",Tools.PLAY);
         sendBroadcast(intent);
         Log.i("TAG", "bn_start: "+"service");
     }

     /**
      * 暂停
      * @param v
      */
     public void bn_pause(View v){
         Intent intent=new Intent("operator.receiver");
         intent.putExtra("cmd",Tools.PAUSE);
         sendBroadcast(intent);
     }

     /**
      * 停止
      * @param v
      */
     public void bn_stop(View v){
         Intent intent=new Intent("operator.receiver");
         intent.putExtra("cmd",Tools.STOP);
         sendBroadcast(intent);
     }

5.通过后台服务的方式，需要在AndroidManifest.xml文件中进行注册

  <service
             android:name=".AudioService"
             android:enabled="true"
             android:exported="true">
         </service>

通过VideoView来播放视频

通过VideoView进行播放视频文件，只需要设置资源URI即可，具体如下：

  private VideoView mVideoView;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_video);
         mVideoView= (VideoView) this.findViewById(R.id.vv_info);
         //设置路径
         File file=new File(Environment.getExternalStorageDirectory(),"DCIM/Camera/VID20190629142614.mp4");
         Log.i("TAG", "onCreate: "+file.getPath());
         if(!file.exists()){
             Log.i("TAG", "onCreate: 文件不存在");
         }
         Uri uri=Uri.fromFile(file);
         mVideoView.setVideoURI(uri);
         //设置Media Controller
         MediaController controller=new MediaController(this);
         mVideoView.setMediaController(controller);
         //获取焦点
         mVideoView.requestFocus();
         mVideoView.start();
         //设置播放完成事件
         mVideoView.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
             @Override
             public void onCompletion(MediaPlayer mp) {
                 Toast.makeText(VideoActivity.this, "播放完毕", Toast.LENGTH_SHORT).show();
             }
         });
     }

通过MediaPlayer来播放视频

通过MediaPlayer来播放视频文件，然后通过SurfaceView来显示视频内容，具体步骤如下：

1.启动，通过setDisplay来设置显示内容

 public  void bn_start(View view)  {
         mMediaPlayer.reset();//到Idle状态
         //设置路径
         File file=new File(Environment.getExternalStorageDirectory(),"DCIM/Camera/VID20190629142614.mp4");
         Log.i("TAG", "onCreate: "+file.getPath());
         if(!file.exists()){
             Log.i("TAG", "onCreate: 文件不存在");
         } else {
             Log.i("TAG", "onCreate: 文件存在 ");
         }
         Uri uri=Uri.fromFile(file);
         try {
             mMediaPlayer.setDataSource(this,uri);
             mMediaPlayer.setDisplay(mSurfaceView.getHolder());
             mMediaPlayer.prepare();
             mMediaPlayer.start();
         } catch (IOException e) {
             e.printStackTrace();
         }
     }

2. 暂停与停止

  public  void bn_pause(View view){
         if(mMediaPlayer.isPlaying()){
             mMediaPlayer.pause();
         }
     }

     public  void bn_stop(View view){
         if(mMediaPlayer.isPlaying()){
             mMediaPlayer.stop();
         }
     }

3. 资源释放

  @Override
     protected void onDestroy() {
         if(mMediaPlayer!=null && mMediaPlayer.isPlaying()){
             mMediaPlayer.stop();
         }
         if(mMediaPlayer!=null){
             mMediaPlayer.release();
             mMediaPlayer=null;
         }
         super.onDestroy();
     }

权限设置

如果要播放视频，需要相应的权限设置，并在安装时获取请求权限

     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
     <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

备注

合抱之木，生于毫末；九层之台，起于垒土；千里之行，始于足下。