为什么自带的函数ENCODE和DECODE出来就有问题？

在做SOAP的时候，发现上传到服务端程序就会有问题，而且都是delphi开发的，编码也是用的自带函数SOAP.endecd，于是在单机上进行测试，代码如下：var
  input_str_stream:TStringStream;
  input_mem_stream:TMemoryStream;
  output_str_stream:TStringStream;
  output_mem_stream:TMemoryStream;  output_file,send_string:string;
begin
  try
      input_mem_stream:=TMemoryStream.Create;
      output_mem_stream:=TMemoryStream.Create;      input_mem_stream.LoadFromFile(edt1.Text); 
      input_mem_stream.SaveToFile('d:\temp_64_oldoutput.jpg');
      input_str_stream:=TStringStream.Create;
      input_mem_stream.SaveToStream(input_str_stream);
      send_string:=EncodeBase64(input_str_stream,Length(input_str_stream.DataString));//编码      output_str_stream:=TStringStream.Create(DecodeBase64(send_string));
      output_mem_stream.LoadFromStream(output_str_stream);
      output_file:='D:\tmp_64_output.jpg';
      output_mem_stream.SaveToFile(output_file);  finally
    input_str_stream.Free;
    input_mem_stream.Free;
    output_str_stream.Free;
    output_mem_stream.Free;  end;结果，源文件和解码出来的文件完全不一样
源文件:00-3F
FFD8FFE000104A4649460001010100
0000000000FFDB0043000806060706
05080707070909080A0C140D0C0B0B
0C1912130F141D1A1F1E1D1A1C1C20
242E2720
编码输出：00-3F
D8BB430048234D02545A0000545A00
000060000048234D02E02653020000
00000000000001000000B004020000
000000080000005400610062004F00
72006400