音频 PCM 数据的采集和播放

PCM（Pulse Code Modulation）脉冲编码调制 —— 音频的采集与量化过程。

PCM数据是最原始的音频数据完全无损，所以PCM数据虽然音质优秀但体积庞大。

为了解决这个问题先后诞生了一系列的音频格式，这些音频格式运用不同的方法对音频数据进行压缩，其中有无损压缩（ALAC、APE、FLAC）和有损压缩（MP3、AAC、OGG、WMA）两种。

代码实现逻辑过程：

使用AudioRecord录制pcm音频 ——> PCM转WAV（只要加上wav头文件即可）——> 使用AudioTrack播放pcm音频

——> 使用 AudioTrack 播放音频

使用AudioRecord录制PCM音频代码：
/**
 * 采样率，现在能够保证在所有设备上使用的采样率是44100Hz, 但是其他的采样率（22050, 16000, 11025）在一些设备上也可以使用。
 */
private static final int SAMPLE_RATE_INHZ = 44100;

/**
 * 声道数。CHANNEL_IN_MONO and CHANNEL_IN_STEREO. 其中CHANNEL_IN_MONO是可以保证在所有设备能够使用的。
 */
private static final int CHANNEL_CONFIG = AudioFormat.CHANNEL_IN_MONO;
/**
 * 返回的音频数据的格式。 ENCODING_PCM_8BIT, ENCODING_PCM_16BIT, and ENCODING_PCM_FLOAT.
 */
private static final int AUDIO_FORMAT = AudioFormat.ENCODING_PCM_16BIT;

final int minBufferSize = AudioRecord.getMinBufferSize(SAMPLE_RATE_INHZ, CHANNEL_CONFIG, AUDIO_FORMAT);
audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLE_RATE_INHZ,
    CHANNEL_CONFIG, AUDIO_FORMAT, minBufferSize);

final byte data[] = new byte[minBufferSize];
final File file = new File(getExternalFilesDir(Environment.DIRECTORY_MUSIC), "test.pcm");
if (!file.mkdirs()) {
    Log.e(TAG, "Directory not created");
}
if (file.exists()) {
    file.delete();
}

audioRecord.startRecording();
isRecording = true;

new Thread(new Runnable() {
    @Override public void run() {

        FileOutputStream os = null;
        try {
            os = new FileOutputStream(file);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

        if (null != os) {
            while (isRecording) {
                int read = audioRecord.read(data, 0, minBufferSize);
                // 如果读取音频数据没有出现错误，就将数据写入到文件
                if (AudioRecord.ERROR_INVALID_OPERATION != read) {
                    try {
                        os.write(data);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
            try {
                Log.i(TAG, "run: close file output stream !");
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}).start();

PCM转WAV：
// 音频数据的大小
long totalAudioLen = fileInputStream.getChannel().size();
// wav总区块大小
long totalDataLen = totalAudioLen + 36;
// 声道数量
int channels;
// 采样率
long longSampleRate;
// 位元率
long byteRate = 16 * longSampleRate * channels / 8;


byte[] header = new byte[44];
        // RIFF/WAVE header
        header[0] = 'R';
        header[1] = 'I';
        header[2] = 'F';
        header[3] = 'F';
        header[4] = (byte) (totalDataLen & 0xff);
        header[5] = (byte) ((totalDataLen >> 8) & 0xff);
        header[6] = (byte) ((totalDataLen >> 16) & 0xff);
        header[7] = (byte) ((totalDataLen >> 24) & 0xff);
        //WAVE
        header[8] = 'W';
        header[9] = 'A';
        header[10] = 'V';
        header[11] = 'E';
        // 'fmt ' chunk
        header[12] = 'f';
        header[13] = 'm';
        header[14] = 't';
        header[15] = ' ';
        // 4 bytes: size of 'fmt ' chunk
        header[16] = 16;
        header[17] = 0;
        header[18] = 0;
        header[19] = 0;
        // format = 1
        header[20] = 1;
        header[21] = 0;
        header[22] = (byte) channels;
        header[23] = 0;
        header[24] = (byte) (longSampleRate & 0xff);
        header[25] = (byte) ((longSampleRate >> 8) & 0xff);
        header[26] = (byte) ((longSampleRate >> 16) & 0xff);
        header[27] = (byte) ((longSampleRate >> 24) & 0xff);
        header[28] = (byte) (byteRate & 0xff);
        header[29] = (byte) ((byteRate >> 8) & 0xff);
        header[30] = (byte) ((byteRate >> 16) & 0xff);
        header[31] = (byte) ((byteRate >> 24) & 0xff);
        // block align
        header[32] = (byte) (2 * 16 / 8);
        header[33] = 0;
        // bits per sample
        header[34] = 16;
        header[35] = 0;
        //data
        header[36] = 'd';
        header[37] = 'a';
        header[38] = 't';
        header[39] = 'a';
        header[40] = (byte) (totalAudioLen & 0xff);
        header[41] = (byte) ((totalAudioLen >> 8) & 0xff);
        header[42] = (byte) ((totalAudioLen >> 16) & 0xff);
        header[43] = (byte) ((totalAudioLen >> 24) & 0xff);

使用AudioTrack 播放音频

/**
     * 播放，使用stream模式
     */
    private void playInModeStream() {
        /*
        * SAMPLE_RATE_INHZ 对应pcm音频的采样率
        * channelConfig 对应pcm音频的声道
        * AUDIO_FORMAT 对应pcm音频的格式
        * */
        int channelConfig = AudioFormat.CHANNEL_OUT_MONO;
        final int minBufferSize = AudioTrack.getMinBufferSize(SAMPLE_RATE_INHZ, channelConfig, AUDIO_FORMAT);
        audioTrack = new AudioTrack(
            new AudioAttributes.Builder()
                .setUsage(AudioAttributes.USAGE_MEDIA)
                .setContentType(AudioAttributes.CONTENT_TYPE_MUSIC)
                .build(),
            new AudioFormat.Builder().setSampleRate(SAMPLE_RATE_INHZ)
                .setEncoding(AUDIO_FORMAT)
                .setChannelMask(channelConfig)
                .build(),
            minBufferSize,
            AudioTrack.MODE_STREAM,
            AudioManager.AUDIO_SESSION_ID_GENERATE);
        audioTrack.play();

        File file = new File(getExternalFilesDir(Environment.DIRECTORY_MUSIC), "test.pcm");
        try {
            fileInputStream = new FileInputStream(file);
            new Thread(new Runnable() {
                @Override public void run() {
                    try {
                        byte[] tempBuffer = new byte[minBufferSize];
                        while (fileInputStream.available() > 0) {
                            int readCount = fileInputStream.read(tempBuffer);
                            if (readCount == AudioTrack.ERROR_INVALID_OPERATION ||
                                readCount == AudioTrack.ERROR_BAD_VALUE) {
                                continue;
                            }
                            if (readCount != 0 && readCount != -1) {
                                audioTrack.write(tempBuffer, 0, readCount);
                            }
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }).start();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    /**
     * 播放，使用static模式
     */
    private void playInModeStatic() {
        // static模式，需要将音频数据一次性write到AudioTrack的内部缓冲区

        new AsyncTask<Void, Void, Void>() {
            @Override
            protected Void doInBackground(Void... params) {
                try {
                    InputStream in = getResources().openRawResource(R.raw.ding);
                    try {
                        ByteArrayOutputStream out = new ByteArrayOutputStream();
                        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;
            }


            @Override
            protected void onPostExecute(Void v) {
                Log.i(TAG, "Creating track...audioData.length = " + audioData.length);

                // R.raw.ding铃声文件的相关属性为 22050Hz, 8-bit, Mono
                audioTrack = new AudioTrack(
                    new AudioAttributes.Builder()
                        .setUsage(AudioAttributes.USAGE_MEDIA)
                        .setContentType(AudioAttributes.CONTENT_TYPE_MUSIC)
                        .build(),
                    new AudioFormat.Builder().setSampleRate(22050)
                        .setEncoding(AudioFormat.ENCODING_PCM_8BIT)
                        .setChannelMask(AudioFormat.CHANNEL_OUT_MONO)
                        .build(),
                    audioData.length,
                    AudioTrack.MODE_STATIC,
                    AudioManager.AUDIO_SESSION_ID_GENERATE);
                Log.d(TAG, "Writing audio data...");
                audioTrack.write(audioData, 0, audioData.length);
                Log.d(TAG, "Starting playback");
                audioTrack.play();
                Log.d(TAG, "Playing");
            }

        }.execute();

    }

demo代码： https://i.cnblogs.com/Files.aspx