Android屏幕镜像三：AudioRecord录制PCM

音频的采集比较简单，可通过AudioRecord实现音频采集，普通应用一般只能采集到麦克风输出的声音（MediaRecorder.AudioSource.MIC），系统应用可以采集系统声音（MediaRecorder.AudioSource.REMOTE_SUBMIX）。

AudioRecord的构造需要以下几个参数：

• 1、audioSource 声音类型，麦克风或系统
• 2、sampleRateInHz 赫兹，赫兹越高声音质量越好，一般是44100 或 48000
• 3、channelConfig 声道，一般是双声道采集
• 4、audioFormat 格式，一般是16位
• 5、bufferSizeInBytes 缓存大小，可通过AudioRecord.getMinBufferSize获取

    // TODO system app use MediaRecorder.AudioSource.REMOTE_SUBMIX
    private static final int AUDIO_RESOURCE = MediaRecorder.AudioSource.MIC;
    private final static int AUDIO_SAMPLE_RATE = 48000;
    private final static int CHANNEL_CONFIG = AudioFormat.CHANNEL_IN_STEREO;
    private final static int AUDIO_FORMAT = AudioFormat.ENCODING_PCM_16BIT;

    private int mAudioResource = AUDIO_RESOURCE;
    private int mAudioSampleRate = AUDIO_SAMPLE_RATE;
    private int mChannelConfig = CHANNEL_CONFIG;
    private int mAudioFormat = AUDIO_FORMAT;
    private int mBufferSizeInBytes;

    this.mBufferSizeInBytes = AudioRecord.getMinBufferSize(mAudioSampleRate, mChannelConfig, mAudioFormat);
    mAudioRecord = new AudioRecord(mAudioResource, mAudioSampleRate, mChannelConfig, mAudioFormat, mBufferSizeInBytes * 2);

初始化完成之后，可通过read方法读取音频数据

    public void startCapture() {
        Log.i(TAG, "startRecord");
        if (mAudioRecord == null) {
            Log.w(TAG, "invalid AudioRecord");
            return;
        }
        //判断AudioRecord的状态是否初始化完毕
        //在AudioRecord对象构造完毕之后，就处于AudioRecord.STATE_INITIALIZED状态了。
        int state = mAudioRecord.getState();
        if (state == AudioRecord.STATE_UNINITIALIZED) {
            Log.w(TAG, "AudioRecord STATE_UNINITIALIZED");
            stopCapture();
            return;
        }
        Log.i(TAG, "startRecording");
        mAudioRecord.startRecording();
        //开启线程读取数据
        mThread = new Thread(mRecordTask);
        mThread.start();
    }

    private Runnable mRecordTask = new Runnable() {
        @Override
        public void run() {
            Log.i(TAG, "recordTask run");
            final byte[] data = new byte[mBufferSizeInBytes];
            isRecording = true;
            while (isRecording) {
                int state;
                if ((state = mAudioRecord.getRecordingState()) != AudioRecord.RECORDSTATE_RECORDING) {
                    Log.i(TAG, "recordTask state: " + state);
                    continue;
                }
                //读取采集数据到缓冲区中，read就是读取到的数据量
                final int read = mAudioRecord.read(data, 0, mBufferSizeInBytes);
                if (AudioRecord.ERROR_INVALID_OPERATION != read && AudioRecord.ERROR_BAD_VALUE != read)
                    try {
                        if (read <= 0) {// != mFrameSize) {
                            try {
                                Thread.sleep(10);
                            } catch (InterruptedException e) {
                                Log.w(TAG, e);
                            }
                            continue;
                        }
                        if (mAudioCallback != null) {
                            mAudioCallback.onCaptureAudioCallback(data);
                        }

                    } catch (Exception e) {
                        Log.w(TAG, e);
                    }
            }
            Log.i(TAG, "recordTask end");
        }
    };

结束录音的时候，关闭AudioRecord

    public void stopCapture() {
        Log.i(TAG, "stopRecord");
        isRecording = false;
        if (mAudioRecord != null) {
            try {
                mAudioRecord.stop();
                Log.i(TAG, "audioRecord.stop()");
            } catch (Exception e) {
                Log.w(TAG, e);
            }
            try {
                mAudioRecord.release();
                Log.i(TAG, "audioRecord.release()");
            } catch (Exception e) {
                Log.w(TAG, e);
            }
        }
    }

通过回调将录制的声音数据回调给调用者，调用者可存储声音数据到文件，通过软件Audacity可播放原始的pcm声音数据。