Loving coroutines & Posix shell help

[Patrick <spell_gooder_now@...>]

I am writing my first program that utilizes corountines and I think they 
are great. Unfortunately they are not supported in so many other 
languages and other places such as the shell. I am writing a program 
that generates graphs as PNGs, encodes them into a video and plays them 
with mplayer,  to generate a live plot and a recording of activity. This 
is all done on the fly.

The problem is I am using to os.execute calls for mencoder and mplayer 
and things are not working reliably. I would like to be able to control 
these last two programs but once a system call is made I can't figure 
out how to throttle the processes it has generated. Does anyone have any 
suggestions on how this could be achieved? I have not used io.popen, I 
can't seem to find much documentation on it but I am assuming the 
processes called by it will still run as fast as they can.

-- Patrick