VirtualDub-mpeg2 Compressed The Movie's Size Automatically

[aspirin_127]

I was used the VirtualDub-MPEG2 1.6.10 to add permanent title to a movie, somehow the total size compressed to almost 1/3 obviously from the original size. In order to ensure the video quality will not decrease, can I keep the original size? some one told me that keep the same bit rate, but how? Thanks!
P.S. The orginal movie has been coded in XVID Mpeg4

[mats.hogberg]

The quality will decrease no matter what, as you have to reencode to get the subtitles rendered.
Bitrate is set under Compression, configure codec (or something to the same effect).
The subtitles by themselves take some bitrate, so using the same bitrate as your source material will surely be too low anyway, for decent result. If at all possible, go for external subs, if your source is already highly compressed like an XviD. I'd recomment permanent subs only if you do a first generation AVI from good source material like a DVD mpg.

/Mats