Well, since you can't do that with managed code, this is probably not the
best place for this question. You will have to implement your encoder in
C/C++. The best place for questions, when it doesn't work is
microsoft.public.windowsce.platbuilder. The best reference to how to do it
is the Platform Builder documentation for the version of Windows CE that
your device is running, but you can probably only get your hands
cost-effectively on 5.0, so get that, read the information on codecs and try
to make a start there.
Paul T.