Step 4 - Bitrate calculation

Introduction

The quality of the final MPEG2 video stream depends on a lot of factors. One important factor is the bitrate - the higher, the better. The higher the bitrate, the more space we'll need for the final files. In other words: We'll now have to weight quality and size against each other and make compromises. We want the final size to exactly fit on a number of CD's, so even though the calculations are very simple, we're better off letting a spreadsheet do these calculations for us.

How to

First Download the Excel spreadsheet.

Don't let the number of columns confuse you - this is just to have a history of the last few calculations (more workspace). They are all identical. The green cells are the ones that you shouldn't need to change very often, if at all. A 74 min. CD can maximally contain 735 MB, while a 80 min. CD can contain up to 795 MB (on SVCD's). I'm not 100% sure about the overhead rate yet, so just leave it for now.

The white cells are the ones you can play around with to calculate the final video bitrate. SVCD supports up to two audio streams, although you normally probably just want one. I recommend 192 or 160 kbps for the main track (max. is 224 kbps), while e.g. a director's comments track can do with 128 kbps, or even 96, 80 or 64 kbps if it's encoded in mono. The most important factor is the number of CD's you want to use.

While you're playing with it, you can see the results in the yellow cells at the bottom. You cannot have an average rate higher than the maximum rate. You can however choose to ignore this calculation and just go for the average bitrate you want (as long as it's equal to or lower than the maximum bitrate), but then you'll end up with something that doesn't exactly fill out a specific number of CD's. I do not recommend bitrates lower than 1600 kbps, but you'll have to judge for yourself.