Android MediaCodec 录制系统音频功能实现完整代码

以下是使用Android的MediaCodec录制系统音频的完整代码：

public class AudioRecorder {
    private static final String TAG = "AudioRecorder";
    private static final String MIME_TYPE = "audio/mp4a-latm";
    private static final int SAMPLE_RATE = 44100;
    private static final int BIT_RATE = 64000;
    private static final int CHANNEL_COUNT = 2;
    private static final int TIMEOUT_US = 10000;

    private MediaCodec mMediaCodec;
    private AudioRecord mAudioRecord;
    private boolean mIsRecording;
    private ByteBuffer[] mInputBuffers;
    private ByteBuffer[] mOutputBuffers;

    public void startRecording(String filePath) throws IOException {
        mMediaCodec = MediaCodec.createEncoderByType(MIME_TYPE);
        MediaFormat format = MediaFormat.createAudioFormat(MIME_TYPE, SAMPLE_RATE, CHANNEL_COUNT);
        format.setInteger(MediaFormat.KEY_BIT_RATE, BIT_RATE);
        mMediaCodec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
        mMediaCodec.start();

        mAudioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLE_RATE,
                CHANNEL_COUNT == 1 ? AudioFormat.CHANNEL_IN_MONO : AudioFormat.CHANNEL_IN_STEREO,
                AudioFormat.ENCODING_PCM_16BIT, AudioRecord.getMinBufferSize(SAMPLE_RATE,
                CHANNEL_COUNT == 1 ? AudioFormat.CHANNEL_IN_MONO : AudioFormat.CHANNEL_IN_STEREO,
                AudioFormat.ENCODING_PCM_16BIT) * 2);

        mAudioRecord.startRecording();
        mIsRecording = true;
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    writeDataToFile(filePath);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

    private void writeDataToFile(String filePath) throws IOException {
        FileOutputStream fos = new FileOutputStream(filePath);
        while (mIsRecording) {
            int inputBufferIndex = mMediaCodec.dequeueInputBuffer(TIMEOUT_US);
            if (inputBufferIndex >= 0) {
                ByteBuffer inputBuffer = mInputBuffers[inputBufferIndex];
                inputBuffer.clear();
                int length = mAudioRecord.read(inputBuffer, inputBuffer.capacity());
                if (length > 0) {
                    mMediaCodec.queueInputBuffer(inputBufferIndex, 0, length, System.nanoTime() / 1000, 0);
                }
            }

            MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
            int outputBufferIndex = mMediaCodec.dequeueOutputBuffer(bufferInfo, TIMEOUT_US);
            while (outputBufferIndex >= 0) {
                ByteBuffer outputBuffer = mOutputBuffers[outputBufferIndex];
                outputBuffer.position(bufferInfo.offset);
                outputBuffer.limit(bufferInfo.offset + bufferInfo.size);
                byte[] chunkAudio = new byte[bufferInfo.size];
                outputBuffer.get(chunkAudio);
                fos.write(chunkAudio);
                mMediaCodec.releaseOutputBuffer(outputBufferIndex, false);
                outputBufferIndex = mMediaCodec.dequeueOutputBuffer(bufferInfo, TIMEOUT_US);
            }
        }
        try {
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        mAudioRecord.stop();
        mAudioRecord.release();
        mMediaCodec.stop();
        mMediaCodec.release();
    }
}

在上述代码中，我们使用了Android的`MediaCodec`和`AudioRecord` API来进行音频录制。在`startRecording()`方法中，我们首先创建了一个`MediaCodec`对象，用于进行编码操作。然后，我们创建了一个`AudioRecord`对象，并按照指定的参数进行了初始化。最后，我们启动了一个新线程，将音频数据写入到指定的文件中。

在`writeDataToFile()`方法中，我们首先从`AudioRecord`对象读取音频数据并将其填充到`MediaCodec`的输入缓冲区中。接下来，我们从`MediaCodec`的输出缓冲区中读取编码后的音频数据，并将其写入到指定的文件中。循环进行上述操作直到停止录制。

需要注意的是，这段代码只是一个简单的示例，还需要根据具体的应用场景进行适当的调整。例如，可以添加错误处理和异常情况的处理逻辑。