播放一帧音频
Android SDK 提供了3套音频播放的API,分别是MediaPlayer(更适合在后台长时间播放本地音乐文件),SoundPool(适合比较短的音频片段,比如游戏声音,按键声),AudioTrack(更接近底层,提供了非常强大的控制能力)
AudioTrack的工作流程
(1)配置参数,初始化内部的音频播放缓冲区
(2)开始播放
(3)需要一个线程,不断地向AudioTrack的缓冲区“写入”音频数据,这个过程也要及时,否则就会出现”underrun“的错误,意味应用层没有及时地“送入”音频数据,导致内部的音频播放缓冲区为null
(4)停止播放,释放资源
AudioTrack(int streamType, int sampleRateInHz, int channelConfig, int audioFormat, int bufferSizeInBytes, int mode)
参数:
1>streamType :这个参数代表当前应用使用的哪种音频管理策略,当系统有多个进程需要播放音频时,这个管理策略会决定最终的展现效果,这个参数可选的值以常量的形式定义在AudioManager类中
STREAM_VOCIE_CALL:电话声音
STREAM_SYSTEM:系统声音
STREAM_RING:铃声
STREAM_MUSCI:音乐声
STREAM_ALARM:警告声
STREAM_NOTIFICATION:通知声
2>sampleRateInHz :采样率的取之范围必须在4000HZ~192000Hz之间
3>channelConfig:通道数的配置,可以选的常量形式定义在AudioFormat类中,常用的是CHANNEL_IN_MINO :(单通道)
CHANNEL_IN_STEREOP(双通道)
4>audioFormat :数据位宽,AudioFormat类中,常用的16BIT ,8BIT
5>bufferSizeInBytes:缓冲区大小,用AudioTrack类中提供的方法获取
6>mode :AudioTrack提供两种播放模式,一种是static方式,一种是streaming方式
static:方式:将所有数据一次性都写入播放缓冲区,简单高效,通常用于播放铃声,系统提醒的音频片段。
streaming方式:按照一定时间间隔不间断地写入音频数据,理论上它可以用于任何音频播放的场景
public class AudioPlayer {private static final String TAG = "AudioPlayer";private static final int DEFAULT_STREAM_TYPE = AudioManager.STREAM_MUSIC;private static final int DEFAULT_SAMPLE_RATE = 44100;private static final int DEFAULT_CHANNEL_CONFIG = AudioFormat.CHANNEL_IN_STEREO;private static final int DEFAULT_AUDIO_FORMAT = AudioFormat.ENCODING_PCM_16BIT;private static final int DEFAULT_PLAY_MODE = AudioTrack.MODE_STREAM;private boolean mIsPlayStarted = false;private int mMinBufferSize = 0;private AudioTrack mAudioTrack; public boolean startPlayer() {return startPlayer(DEFAULT_STREAM_TYPE,DEFAULT_SAMPLE_RATE,DEFAULT_CHANNEL_CONFIG,DEFAULT_AUDIO_FORMAT);}public boolean startPlayer(int streamType, int sampleRateInHz, int channelConfig, int audioFormat) {if (mIsPlayStarted) {Log.e(TAG, "Player already started !");return false;}mMinBufferSize = AudioTrack.getMinBufferSize(sampleRateInHz,channelConfig,audioFormat);if (mMinBufferSize == AudioTrack.ERROR_BAD_VALUE) {Log.e(TAG, "Invalid parameter !");return false;}Log.d(TAG , "getMinBufferSize = "+mMinBufferSize+" bytes !");mAudioTrack = new AudioTrack(streamType,sampleRateInHz,channelConfig,audioFormat,mMinBufferSize,DEFAULT_PLAY_MODE);if (mAudioTrack.getState() == AudioTrack.STATE_UNINITIALIZED) {Log.e(TAG, "AudioTrack initialize fail !");return false;} mIsPlayStarted = true;Log.d(TAG, "Start audio player success !");return true;}public int getMinBufferSize() {return mMinBufferSize;}public void stopPlayer() {if (!mIsPlayStarted) {return;}if (mAudioTrack.getPlayState() == AudioTrack.PLAYSTATE_PLAYING) {mAudioTrack.stop(); }mAudioTrack.release();mIsPlayStarted = false;Log.d(TAG, "Stop audio player success !");}public boolean play(byte[] audioData, int offsetInBytes, int sizeInBytes) {if (!mIsPlayStarted) {Log.e(TAG, "Player not started !");return false;}if (sizeInBytes < mMinBufferSize) {Log.e(TAG, "audio data is not enough !");return false;}if (mAudioTrack.write(audioData,offsetInBytes,sizeInBytes) != sizeInBytes) { Log.e(TAG, "Could not write all the samples to the audio device !");} mAudioTrack.play();Log.d(TAG , "OK, Played "+sizeInBytes+" bytes !");return true;}
}