8.Media and Camera/Media Playback

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1.Media Palyback

　　The Android multimedia framework includes support for playing variety of common media types, so that you can easily integrate audio, video

　　　　and images into your applications.

　　You can play audio or video from media files stored in your application‘s resources (raw resources), from standalone files in the filesystem,

　　　　or from a data stream arriving over a network connection, all using MediaPlayer APIs.

2. The Basic

　　MediaPlayer ---> Primary API for Playing sound and video

　　AudioManager ---> managers audio sources and audio output on a device

3. Manifest Declarations

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

　　<uses-permission android:name="android.permission.WAKE_LOCK" /> : keep the screen from dimming or the processor from sleeping

4. Using MediaPalyer

　　An object of this class can fetch, decode, and play both audio and video with minimal setup. It supports several different media sources

　　　　such as:

　　　　<1>Local resources

　　　　　　Here is an simple example of how to play audio

　　　　　　<i> place a local resources saved in res/raw/ directory

　　　　　　<ii>

MediaPlayer mediaPlayer = MediaPlayer.create(getApplication(),R.raw.beatiful_girl);        mediaPlayer.start();

　　　　<2>Internal URIs, such as one you might obtain from a Content Resolver

Uri myUri = ....; // initialize Uri here, obtained through Content ResolverMediaPlayer mediaPlayer = new MediaPlayer();mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);mediaPlayer.setDataSource(getApplicationContext(), myUri);mediaPlayer.prepare();mediaPlayer.start();

　　　　<3>External URLs(streaming)

String url = "http://........"; // your URL hereMediaPlayer mediaPlayer = new MediaPlayer();mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);mediaPlayer.setDataSource(url);mediaPlayer.prepare(); // might take long! (for buffering, etc)mediaPlayer.start();

 

　　4.1 Asynchronous Preparation

　　　　important to keep in mind:

　　　　<1> the call to prepare() can take a long time to excute, because it might involve fetching and decoding media data.

　　　　　　 　　So, never call it from application`s UI thread. 

　　　　<2> framework supplies a convinient way to accomplish this task by using prepareAsync() method

　　　　　　 When the media is done preparing, the onPrepared() method of the MediaPlayer.OnPreparedListener, configured through

　　　　　　　　setOnPreparedListener() is called.

　　4.2 Managing State

　　　　

　　4.3 Releasing the MediaPlayer

　　　　A MediaPlayer can consume valuable system resources. Therefore, you should call release() to make sure any  system resources

　　　　　　allocated toit are properly released　

mediaPlayer.release();mediaPlayer = null;

　　　　As an example, consider the problems that could happen if you forgot to release the MediaPlayer when your activity is stopped, but

　　　　　　create a new one when the activity starts again. As you may know, when the user changes the screen orientation (or changes the

　　　　　　device configuration in another way), the system handles that by restarting the activity (by default), so you might quickly consume

　　　　　　all of the system resources as the user rotates the device back and forth between portrait and landscape, because at each

　　　　　　orientation change, you create a new MediaPlayer that you never release.

 

5. Using a Service with MediaPlayer

　　If you want your media to play in the background even when your application is not onscreen—that is, you want it to continue playing

　　　　while the user is interacting with other applications—then you must start a Service and control the MediaPlayer instance from there.

　　5.1 Running asynchronousyly

　　　　First of all, like an Activity, all work in a Service is done in a single thread by default. 

　　　　if you are running an activity and a service from the same application("main thread") by default,

　　　　Therefore, services needs to process incoming intents quickly and never perform lengthly computatipons when responding to them.

 

　　　　If any heavy work or blocking calls are expected, you must do those tasks asynchronously:

　　　　　　either from another thread you implement yourself, or using the framework‘s many facilities for asynchronous processing.

 

8.Media and Camera/Media Playback