如何在android Surfaceview中从视频中获取当前帧？

public class MySurfaceView extends SurfaceView implements SurfaceHolder.Callback {
    private MediaPlayer mediaPlayer;

    public MySurfaceView(Context context) {
        super(context);
        getHolder().addCallback(this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mediaPlayer = new MediaPlayer();
        mediaPlayer.setDisplay(holder);
        mediaPlayer.setDataSource("视频文件路径");
        mediaPlayer.prepareAsync();

        mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
            @Override
            public void onPrepared(MediaPlayer mp) {
                mediaPlayer.start();
            }
        });
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mediaPlayer.release();
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        // 空实现
    }

    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);

        if (mediaPlayer != null && mediaPlayer.isPlaying()) {
            Canvas surfaceCanvas = getHolder().lockCanvas();
            if (surfaceCanvas != null) {
                surfaceCanvas.drawBitmap(yourBitmap, 0, 0, null);
                getHolder().unlockCanvasAndPost(surfaceCanvas);
            }
        }
    }
}