Opening a TStream on stdin/stdout in a Delphi console app

I'm trying to write a Delphi console application that creates a TStream for its standard input, and another TStream for its standard output.

(It will be launched by a host app with its input and output redirected to pipes, and will be passing binary data to/from that host app, so TStream will be much better-suited to the task than ReadLn/WriteLn.)

How do I go about opening a TStream on standard input or standard output?