You can use Camera.setMode and Camera.setQuality:
camera.setMode(320,240,20,false); // set size here
camera.setQuality(0,90); // this favors quality over bandwidth
This is as exact as you can get using Flash plugin as the encoder. You should be able to get better quality from the same camera with a dedicated encoder.
Note, don’t set the 2nd arg of setQuality (quality setting) above 90. It is known to be a problem.
Richard