gistfile1.cs

            using (var fs = new FileStream(path, FileMode.Open, FileAccess.Read)) {
                using (var br = new BinaryReader(fs, new ASCIIEncoding())) {
                    // UnityWeb
                    while (br.ReadChar() != 0) {
                        ;
                    }
                    // format
                    br.ReadInt32();
                    // player version
                    while (br.ReadChar() != 0) {
                        ;
                    }
                    // engine version
                    while (br.ReadChar() != 0) {
                        ;
                    }
                    // file size
                    br.ReadInt32();
                    // data offset
                    var bytes = br.ReadBytes(4);
                    int dataOffset = bytes[3] | (bytes[2] << 8) | (bytes[1] << 16) | (bytes[0] << 24);

                    br.BaseStream.Seek(dataOffset, SeekOrigin.Begin);

                    // LZMA props
                    br.ReadBytes(5);
                    // size
                    size = (int) br.ReadInt64();