silverlight MediaElement截取当前帧

需求：从播放器上截取出当前帧，提交到服务器/或吐给javascript

1、从当前的MediaElement上创建WriteableBitmap

WriteableBitmap bitmap = new WriteableBitmap(this.Player,@R_874_6633@

2、从WriteableBitmap编码成jpg格式

public static void SavePicToStream(WriteableBitmap bitmap,Stream stream)
        {
            int width = bitmap.pixelWidth;
            int height = bitmap.pixelHeight;
            int bands = 3;
            byte[][,] raster = new byte[bands][,];  //用来保存bitmap中每个像素点的RGB分量的数组  
            for (int i = 0; i < bands; i++)
            {
                raster[i] = new byte[width,height];
            }
            for (int row = 0; row < height; row++)
            {
                for (int column = 0; column < width; column++)
                {
                    int pixel = bitmap.pixels[width * row + column];
                    raster[0][column,row] = (bytE)(pixel >> 16);  //R  
                    raster[1][column,row] = (bytE)(pixel >> 8);   //G  
                    raster[2][column,row] = (bytE)pixel;          //B  
                }
            }
            FluxJpeg.Core.ColorModel model = new FluxJpeg.Core.ColorModel { colorspace = FluxJpeg.Core.ColorSpace.RGB };
            FluxJpeg.Core.Image img = new FluxJpeg.Core.Image(model,raster);

            FluxJpeg.Core.Encoder.JpegEncoder encoder = new FluxJpeg.Core.Encoder.JpegEncoder(img,100,stream);
            encoder.Encode();
        }  

public String GetCurrentImageBase64String()
        {
            var stream = new MemoryStream();
            Tools.SavePicToStream(this.GetCurrentImage(),stream);
            stream.Seek(0,SeekOrigin.begin);
            var binaryData = new Byte[stream.Length];
            long bytesRead = stream.Read(binaryData,(int)stream.Length);
            String t = Convert.ToBase64String(binaryData);
            return t;
        }

注意：视频文件和XaP必须在同一个域，否则将出现WriteableBitmap的Pixels受保护，无法读。（出于版权保护的原因）

微软MSDN给出的解释如下：

受保护的内容