In 2 pass, the 2nd pass corrects the 1st pass. You get a better overall picture, but that depends on your source and type of bit rate. The bad is it takes twice as long, but it is a better render almost all the time.

If the video is under 74 minutes and you're using 192kbps .AC3 audio, you can just use CBR at a rate of 8 megabits/sec and the encode will be the highest quality it can be.

Two pass is only really valid when you use variable bit rate (VBR) because you need to fit more than 74 minutes on a single layer disc. Using VBR, you set a minimum, maximum and average bitrate. The average bit rate determines the final file size. On the first pass, the encoder analyzes the file looking for places which need a higher bit rate, like those parts with high motion, very fine detail or video noise. It also looks for parts of the video which don't need as high a bit rate and allocates the bits it can save from these parts to the parts which need them.

It's a balancing act, take bits from here and allocate them there and over the length of the entire file make sure that the bit rate hits the average that you set.

If you need a bit rate calculator, try this one:

Bitcalc110.zip

John