Android MediaCodec录屏时同时录制系统音频功能实现代码

在 Android 上录制屏幕并同时录制系统音频可以通过使用 MediaCodec 和 MediaProjection 来实现。下面是一个简单的示例代码：

public class ScreenRecorder {
    private static final String TAG = "ScreenRecorder";

    private static final String MIME_TYPE = "video/avc";
    private static final int FRAME_RATE = 30;
    private static final int I_FRAME_INTERVAL = 10;
    private static final int BIT_RATE = 6000000;
    private static final int TIMEOUT_US = 10000;

    private MediaProjection mMediaProjection;
    private MediaCodec mMediaCodec;
    private VirtualDisplay mVirtualDisplay;
    private Surface mInputSurface;
    private boolean mIsRecording;

    private AudioRecord mAudioRecord;
    private Thread mAudioThread;
    private boolean mIsAudioRecording;

    public void startRecording(Context context, MediaProjection mediaProjection) throws IOException {
        mMediaProjection = mediaProjection;

        // 初始化 MediaCodec
        MediaFormat format = MediaFormat.createVideoFormat(MIME_TYPE, displayWidth, displayHeight);
        format.setInteger(MediaFormat.KEY_COLOR_FORMAT, MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface);
        format.setInteger(MediaFormat.KEY_BIT_RATE, BIT_RATE);
        format.setInteger(MediaFormat.KEY_FRAME_RATE, FRAME_RATE);
        format.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, I_FRAME_INTERVAL);
        mMediaCodec = MediaCodec.createEncoderByType(MIME_TYPE);
        mMediaCodec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
        mInputSurface = mMediaCodec.createInputSurface();
        mMediaCodec.start();

        // 创建 VirtualDisplay
        mVirtualDisplay = mMediaProjection.createVirtualDisplay(TAG,
                displayWidth, displayHeight, displayDensity,
                DisplayManager.VIRTUAL_DISPLAY_FLAG_PUBLIC,
                mInputSurface, null, null);

        // 启动音频录制
        startAudioRecording();

        mIsRecording = true;
    }

    public void stopRecording() {
        mIsRecording = false;

        // 停止音频录制
        stopAudioRecording();

        if (mMediaProjection != null) {
            mMediaProjection.stop();
            mMediaProjection = null;
        }
        if (mVirtualDisplay != null) {
            mVirtualDisplay.release();
            mVirtualDisplay = null;
        }
        if (mMediaCodec != null) {
            mMediaCodec.stop();
            mMediaCodec.release();
            mMediaCodec = null;
        }
        if (mInputSurface != null) {
            mInputSurface.release();
            mInputSurface = null;
        }
    }

    private void startAudioRecording() {
        int sampleRate = AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_SYSTEM);
        int minBufferSize = AudioRecord.getMinBufferSize(sampleRate, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT);
        mAudioRecord = new AudioRecord(MediaRecorder.AudioSource.REMOTE_SUBMIX, sampleRate,
                AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT, minBufferSize);

        mIsAudioRecording = true;
        mAudioThread = new Thread(new Runnable() {
            @Override
            public void run() {
                byte[] buffer = new byte[minBufferSize];
                while (mIsAudioRecording) {
                    int readSize = mAudioRecord.read(buffer, 0, minBufferSize);
                    if (readSize > 0) {
                        ByteBuffer[] inputBuffers = mMediaCodec.getInputBuffers();
                        int inputBufferIndex = mMediaCodec.dequeueInputBuffer(TIMEOUT_US);
                        if (inputBufferIndex >= 0) {
                            ByteBuffer inputBuffer = inputBuffers[inputBufferIndex];
                            inputBuffer.clear();
                            inputBuffer.put(buffer);
                            long pts = System.nanoTime() / 1000;
                            mMediaCodec.queueInputBuffer(inputBufferIndex, 0, readSize, pts, 0);
                        }
                    }
                }
                mAudioRecord.stop();
                mAudioRecord.release();
                mAudioRecord = null;
            }
        });
        mAudioThread.start();
        mAudioRecord.startRecording();
    }

    private void stopAudioRecording() {
        mIsAudioRecording = false;
        try {
            mAudioThread.join();
        } catch (InterruptedException e) {
            Log.e(TAG, "stopAudioRecording: ", e);
        }
    }
}

需要注意的是，上述代码中的 `AudioRecord` 使用了 `MediaRecorder.AudioSource.REMOTE_SUBMIX`，这是一种特殊的音频源，可以录制系统音频。但是并不是所有的设备都支持 `REMOTE_SUBMIX`，如果你的设备不支持，那么你就无法录制系统音频了。