Encoding 2-Pass VBR?

Dear all

I'm currently using a simple encoding implementation based on the 
encoding example delivered with theora.
Now i tried to change the quality of the output file. Its my 
understanding, that either a bitrate can be set for Constant Bitrate 
(CBR) encoding, or a quality (0-63) for Variable Bitrate (VBR).

As you might know, the basic Encoder Example uses the so-called 2-Pass 
method for encoding. As a comment in the example code suggests, a 
"estimated bitrate" must be set for the 2-pass method to success.

My code runs smoothly when I set a bitrate, but then the quality 
parameter seems useless. When I try to run the 2-pass method with 
bitrate=0 (--> VBR) and a quality between 0-63, my implementation will 
crash though.
Is there any possibility to run the existing 2-pass method with the 0-63 
range quality parameter? Thank you for your suggestions.

Kind regards,
Stefan