本篇介绍

本篇介绍下AudioTrack和AudioRecord的使用，通过AudioRecord录音，通过AudioTrack播放录制的音频。

AudioRecord的使用

AudioRecord负责采集音频，下面是一个录音的例子：

    private void startRecord() {
        int sampleRate = 44100;
        int bufferSize = AudioRecord.getMinBufferSize(sampleRate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_8BIT);
        recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, 44100, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_8BIT, bufferSize);
        recorder.startRecording();
        currentState = 0;
        Log.d(TAG, "start record");
        executorService.submit(new Runnable() {
            @Override
            public void run() {
                byte byteBuffer [] = new byte[1024];
                FileOutputStream outputStream = null;
                try {
                    outputStream = new FileOutputStream(PCM_FILE);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                    return;
                }
                while (currentState != 1) {
                    int read = recorder.read(byteBuffer, 0, byteBuffer.length);
                    Log.d(TAG, "size is " + read);
                    try {
                        outputStream.write(byteBuffer, 0, read);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                try {
                    outputStream.flush();
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                recorder.stop();
            }
        });
    }

先创建一个AudioRecord，创建的时候需要指定音频源，采集频率，采集位数，声道数，还有buffer大小，AUdioRecord提供了专门的方法来计算buffer大小。创建好后，调用startRecording就可以采集了。具体采集需要在单独的线程里面做，调用AudioRecord的read就可以，读出来的内容就是采集的数据，这儿是写到了一个文件里面。

AudioTrack的使用

AudioTrack负责播放pcm数据，下面的代码是将刚采集的pcm播放出来

 AudioAttributes audioAttributes = new AudioAttributes.Builder().setContentType(AudioAttributes.CONTENT_TYPE_MUSIC).setUsage(AudioAttributes.USAGE_MEDIA).build();
        AudioFormat audioFormat = new AudioFormat.Builder().setEncoding(AudioFormat.ENCODING_PCM_8BIT).setSampleRate(44100).setChannelMask(AudioFormat.CHANNEL_OUT_MONO).build();
        int bufferSize = AudioTrack.getMinBufferSize(44100, AudioFormat.CHANNEL_OUT_MONO, AudioFormat.ENCODING_PCM_8BIT);
        tracker = new AudioTrack(audioAttributes, audioFormat, bufferSize, AudioTrack.MODE_STREAM, AudioManager.AUDIO_SESSION_ID_GENERATE);
        tracker.play();
        currentState = 2;
        executorService.submit(new Runnable() {
            @Override
            public void run() {
                byte[] data = new byte[1024]; // small buffer size to not overflow AudioTrack's internal buffer
                FileInputStream fileInputStream = null;
                try {
                    fileInputStream = new FileInputStream(new File(PCM_FILE));
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
                int readSize = 0;
                while (readSize != -1) {
                    try {
                        readSize = fileInputStream.read(data);
                    } catch (IOException e) {
                        e.printStackTrace();
                        continue;
                    }
                    Log.d(TAG, "start play read size is " + readSize);
                    if (readSize > 0) {
                        tracker.write(data, 0, readSize);
                    }
                }
                try {
                    fileInputStream.close();
                }
                catch (IOException e) {
                    // handle exception
                }

                tracker.stop();
                tracker.release();
            }
        });

首先是创建AudioTrack，也是需要指定采集位数，采集频率，输出声道，播放buffer，然后调用play就可以播放了，具体的播放就是在单独线程里面调用AudioTrack的write即可。

查看pcm数据

使用audacity就可以查看pcm数据，(下载路径 https://www.audacityteam.org/)
效果如下：

image.png
完整代码路径(https://github.com/leehaoran/opengl/tree/main/audioexample)