Android⾳视频开发（三）：使⽤AudioTrack播放PCM⾳频⼀、AudioTrack 基本使⽤AudioTrack 类可以完成Android平台上⾳频数据的输出任务。
AudioTrack有两种数据加载模式（MODE_STREAM和MODE_STATIC），对应的是数据加载模式和⾳频流类型，对应着两种完全不同的使⽤场景。
MODE_STREAM：在这种模式下，通过write⼀次次把⾳频数据写到AudioTrack中。
这和平时通过write系统调⽤往⽂件中写数据类似，但这种⼯作⽅式每次都需要把数据从⽤户提供的Buffer中拷贝到AudioTrack内部的Buffer中，这在⼀定程度上会使引⼊延时。
为解决这⼀问题，AudioTrack就引⼊了第⼆种模式。
MODE_STATIC：这种模式下，在play之前只需要把所有数据通过⼀次write调⽤传递到AudioTrack中的内部缓冲区，后续就不必再传递数据了。
这种模式适⽤于像铃声这种内存占⽤量较⼩，延时要求较⾼的⽂件。
但它也有⼀个缺点，就是⼀次write的数据不能太多，否则系统⽆法分配⾜够的内存来存储全部数据。
1.1 MODE_STATIC模式MODE_STATIC模式输出⾳频的⽅式如下（注意：如果采⽤STATIC模式，须先调⽤write写数据，然后再调⽤play。
）：public class AudioTrackPlayerDemoActivity extends Activity implementsOnClickListener {private static final String TAG = "AudioTrackPlayerDemoActivity";private Button button;private byte[] audioData;private AudioTrack audioTrack;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);super.setContentView(yout.main);this.button = (Button) super.findViewById(R.id.play);this.button.setOnClickListener(this);this.button.setEnabled(false);new AsyncTask<Void, Void, Void>() {@Overrideprotected Void doInBackground(Void... params) {try {InputStream in = getResources().openRawResource(R.raw.ding);try {ByteArrayOutputStream out = new ByteArrayOutputStream(264848);for (int b; (b = in.read()) != -1;) {out.write(b);}Log.d(TAG, "Got the data");audioData = out.toByteArray();} finally {in.close();}} catch (IOException e) {Log.wtf(TAG, "Failed to read", e);}return null;}@Overrideprotected void onPostExecute(Void v) {Log.d(TAG, "Creating track...");button.setEnabled(true);Log.d(TAG, "Enabled button");}}.execute();}public void onClick(View view) {this.button.setEnabled(false);this.releaseAudioTrack();this.audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, 44100,AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_16BIT,audioData.length, AudioTrack.MODE_STATIC);Log.d(TAG, "Writing audio data...");this.audioTrack.write(audioData, 0, audioData.length);Log.d(TAG, "Starting playback");audioTrack.play();Log.d(TAG, "Playing");this.button.setEnabled(true);}private void releaseAudioTrack() {if (this.audioTrack != null) {Log.d(TAG, "Stopping");audioTrack.stop();Log.d(TAG, "Releasing");audioTrack.release();Log.d(TAG, "Nulling");}}public void onPause() {super.onPause();this.releaseAudioTrack();}}1.2 MODE_STREAM模式MODE_STREAM 模式输出⾳频的⽅式如下：byte[] tempBuffer = new byte[bufferSize];int readCount = 0;while (dis.available() > 0) {readCount = dis.read(tempBuffer);if (readCount == AudioTrack.ERROR_INVALID_OPERATION || readCount == AudioTrack.ERROR_BAD_VALUE) {continue;}if (readCount != 0 && readCount != -1) {audioTrack.play();audioTrack.write(tempBuffer, 0, readCount);}}⼆、AudioTrack 详解2.1 ⾳频流的类型在AudioTrack构造函数中，会接触到AudioManager.STREAM_MUSIC这个参数。
