思路：

我的实时视频流需要加水印，我的解决思路是：将水印图片转换成YUV格式，在Camera中onPreviewFrame中将获取到的视频流做一个叠加

1：水印转YUV

//从drawble中获取水印图片
Bitmap bmp1 = BitmapFactory.decodeResource(App.getCtx().getResources(), R.drawable.ic_camera );
//缩小图片
final Bitmap bmp=scaleImage(bmp1,40,40);
//转YUV
final byte[] mark=getYUVByBitmap(bmp);

2：叠加

int startY=100;//水印Y轴的位置
int startX=100;//水印X轴的位置
mCamera.setPreviewCallback(new Camera.PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {
            int j=0;

            for(int i=startY; i<bmp.getHeight()+startY; i++) {
                for(int c=0;c<bmp.getWidth();c++){
           //去掉PNG水印的黑边    
if(mark[j*bmp.getWidth()+c]!=0x10&&mark[j*bmp.getWidth()+c]!=0x80&&mark[j*bmp.getWidth()+c]!=0xeb){
                       System.arraycopy(mark,j*bmp.getWidth()+c,data,startX+i*1280+c,1);
                   }
                }

                j++;
            }

PS:获取图片YUV所需的方法

//缩小图片到制定长宽
public static Bitmap scaleImage(Bitmap bm, int newWidth, int newHeight)
{
    if (bm == null)
    {
        return null;
    }
    int width = bm.getWidth();
    int height = bm.getHeight();
    float scaleWidth = ((float) newWidth) / width;
    float scaleHeight = ((float) newHeight) / height;
    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth, scaleHeight);
    Bitmap newbm = Bitmap.createBitmap(bm, 0, 0, width, height, matrix,
            true);
    if (bm != null & !bm.isRecycled())
    {
        bm.recycle();
        bm = null;
    }
    return newbm;
}

//图片转YUV
public byte[] getYUVByBitmap(Bitmap bitmap) {
    if (bitmap == null) {
        return null;
    }
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();

    int size = width * height;

    int pixels[] = new int[size];
    bitmap.getPixels(pixels, 0, width, 0, 0, width, height);
    byte[] data = rgb2YCbCr420(pixels, width, height);

    return data;
}

   public static byte[] rgb2YCbCr420(int[] pixels, int width, int height) {
    int len = width * height;
     //yuv格式数组大小，y亮度占len长度，u,v各占len/4长度。
    byte[] yuv = new byte[len * 3 / 2];
    int y, u, v;
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            //屏蔽ARGB的透明度值
            int rgb = pixels[i * width + j] & 0x00FFFFFF;
           //像素的颜色顺序为bgr，移位运算。
            int r = rgb & 0xFF;
            int g = (rgb >> 8) & 0xFF;
            int b = (rgb >> 16) & 0xFF;
           //套用公式
            y = ((66 * r + 129 * g + 25 * b + 128) >> 8) + 16;
            u = ((-38 * r - 74 * g + 112 * b + 128) >> 8) + 128;
            v = ((112 * r - 94 * g - 18 * b + 128) >> 8) + 128;

            y = y < 16 ? 16 : (y > 255 ? 255 : y);
            u = u < 0 ? 0 : (u > 255 ? 255 : u);
            v = v < 0 ? 0 : (v > 255 ? 255 : v);
            //赋值
            yuv[i * width + j] = (byte) y;
            yuv[len + (i >> 1) * width + (j & ~1) + 0] = (byte) u;
            yuv[len + +(i >> 1) * width + (j & ~1) + 1] = (byte) v;
        }
    }
    return yuv;
}

此水印为黑白色，需要彩色的还需自行将bitmap转YUV