how to convert var to bytes array in wp7
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i want to convert vedio into bytes array..
so i want to convert var into bytes array for upload 

var videoInput = new Uri("/uploadNewVideo;component/test.mp4", UriKind.Relative);


tring to upload byte array as parameter to php 
 string a = "TRIAL";
            string url = "phpURL?";
            client.DownloadStringAsync(new Uri(url + "&uploadedfile=" + bytearray + "&name=" + a  ));