Welcome cheersm8,
From what I understand you need to visit this
thread.
There you will find a GREAT tool made up by Kwag that, based on some figures you'll have
to provide, will calculate the amount of compression the video part needs.
It will also start encoding when the correct value is reached if you want.
Be patient with the tool because at 1st it might seem a little difficult to understand how it works.
Be a sports and read Kwag's usage instructions on the
sticky.
If you need help with it post there, ok?
Cheers