function IsUnicodeStream(const Stm: Classes.TStream): Boolean;
var
  StmPos: LongInt;      // current position in stream
  UnicodeMarker: Word;  // marker that indicates a unicode stream
begin
  // Record current location in stream
  StmPos := Stm.Position;
  // Check if stream large enough to contain unicode marker
  if StmPos <= Stm.Size - SizeOf(Word) then
  begin
    // Read first word and check if it is the unicode marker
    Stm.ReadBuffer(UnicodeMarker, SizeOf(UnicodeMarker));
    Result := (UnicodeMarker = $FEFF);
    // Restore stream positions
    Stm.Position := StmPos;
  end
  else
    // Stream too small: can't be unicode
    Result := False;
end;
//delphi/2231