android 10 MediaRecorder录像成mp4文件，视频添加时间水印的实现方式

可以通过以下步骤实现在录制视频时添加时间水印：

1. 创建一个自定义的SurfaceView，用于预览和录制视频。

2. 在SurfaceView的回调函数中创建MediaRecorder对象，并设置相关参数：

mMediaRecorder = new MediaRecorder();
mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
mMediaRecorder.setVideoSize(1280, 720);
mMediaRecorder.setVideoFrameRate(30);
mMediaRecorder.setVideoEncodingBitRate(3 * 1024 * 1024);
mMediaRecorder.setOutputFile(mOutputFile.getAbsolutePath());
mMediaRecorder.setOrientationHint(rotation);

3. 在录制视频之前，创建一个Canvas对象，通过drawText方法在Canvas上绘制当前时间，再将Canvas中的Bitmap作为水印覆盖到SurfaceView上。可以使用Handler定时更新时间水印。

4. 在录制视频开始后，通过MediaCodec将SurfaceView中的内容编码为视频流，并将视频流写入文件中。同时，每次绘制时间水印时，也将SurfaceView的内容编码为视频流，并写入文件中。

5. 录制完成后，释放MediaRecorder和Canvas对象。

完整代码示例：

public class MainActivity extends AppCompatActivity implements SurfaceHolder.Callback {
    private static final String TAG = "MainActivity";
    private static final int PERMISSION_REQUEST_CODE = 1;

    private SurfaceView mSurfaceView;
    private SurfaceHolder mSurfaceHolder;
    private MediaRecorder mMediaRecorder;
    private File mOutputFile;

    private boolean mIsRecording = false;

    private int mRotation;
    private Bitmap mWatermarkBitmap;
    private Paint mWatermarkPaint;

    private Handler mHandler = new Handler();
    private Runnable mUpdateWatermarkRunnable = new Runnable() {
        @Override
        public void run() {
            updateWatermark();
            mHandler.postDelayed(this, 1000);
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mSurfaceView = findViewById(R.id.surface_view);
        mSurfaceHolder = mSurfaceView.getHolder();
        mSurfaceHolder.addCallback(this);

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED
                || ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.CAMERA},
                    PERMISSION_REQUEST_CODE);
        }
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mWatermarkPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mWatermarkPaint.setColor(Color.WHITE);
        mWatermarkPaint.setTextSize(40);
        mWatermarkPaint.setTextAlign(Paint.Align.CENTER);

        mWatermarkBitmap = Bitmap.createBitmap(1280, 720, Bitmap.Config.ARGB_8888);

        mHandler.post(mUpdateWatermarkRunnable);
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        mRotation = getWindowManager().getDefaultDisplay().getRotation();
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mHandler.removeCallbacks(mUpdateWatermarkRunnable);
        releaseMediaRecorder();
    }

    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn_record:
                if (!mIsRecording) {
                    startRecording();
                } else {
                    stopRecording();
                }
                break;
        }
    }

    private void updateWatermark() {
        Canvas canvas = new Canvas(mWatermarkBitmap);
        canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss", Locale.getDefault());
        String time = sdf.format(new Date());

        canvas.drawText(time, 640, 360, mWatermarkPaint);

        Canvas surfaceCanvas = mSurfaceHolder.lockCanvas();
        surfaceCanvas.drawBitmap(mWatermarkBitmap, 0, 0, null);
        mSurfaceHolder.unlockCanvasAndPost(surfaceCanvas);
    }

    private void startRecording() {
        try {
            mIsRecording = true;
            mOutputFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM),
                    "video_" + System.currentTimeMillis() + ".mp4");

            mMediaRecorder = new MediaRecorder();
            mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
            mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
            mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
            mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
            mMediaRecorder.setVideoSize(1280, 720);
            mMediaRecorder.setVideoFrameRate(30);
            mMediaRecorder.setVideoEncodingBitRate(3 * 1024 * 1024);
            mMediaRecorder.setOutputFile(mOutputFile.getAbsolutePath());
            mMediaRecorder.setOrientationHint(mRotation);
            mMediaRecorder.prepare();

            mMediaRecorder.start();
        } catch (IOException e) {
            Log.e(TAG, "startRecording: ", e);
        }
    }

    private void stopRecording() {
        mIsRecording = false;
        releaseMediaRecorder();
    }

    private void releaseMediaRecorder() {
        if (mMediaRecorder != null) {
            mMediaRecorder.stop();
            mMediaRecorder.reset();
            mMediaRecorder.release();
            mMediaRecorder = null;
        }
    }
}

注意：本示例中仅提供了添加时间水印的实现方式，如需完整的录像功能还需要添加权限申请、录制按钮等相关逻辑。