How to encrypt large files using SynCrypto?

SynCrypto is an open source data encryption library for Delphi and FPC included in SynPDF.

I use this code for file encryption:

var
  inputfile : RawByteString;
  outputfile: RawByteString;
begin
  inputfile := StringFromFile('c:\test1.mp4');
  outputfile := TAESCFB.SimpleEncrypt(inputfile,'TEST',true,true);
  FileFromString(outputfile,'c:\test2.mp4');
end;

However it doesn't work for large files (>1GB). Is there any way to encrypt large files?