[Feature Request] Global first and second passes

Hi @ all !

Sometimes I have to encode a ~26 files pack (episodes) and define a 
total size (4.7GB). Actually I define a "static" file size (eg. 4700 / 
26 = 180MB per file).
But this is not really optimized for obtaining a constant quality 
because some episodes needs more bitrate than other ones.

This is why I think there is a needed feature on XviD we could call 
"segmented passes" or "global pass".

We need the ability to concatenate a "first pass file" with another 
"first pass file" and then we will be able to define a global size for 
all the segments (4700 MB).
Then @ second pass, XviD encoder will have to read our "big first pass 
file" and output these segments.

example :
- 01.avi (190MB)
- 02.avi (150MB)
- ....
- 26.avi (200MB)
TOTAL : 4700 MB