How to calculate video data rates from specified file sizes

An algebra refresher for post-production professionals

It strikes me that many post-production professionals get tripped up by a very specific request: Hey, can you get me a copy of this video that’s only [some number] MB?

It seems simple enough, but it requires going all the way back to basic algebra, along with understanding unit conversions, which pop up in all sorts of STEM fields.

What to measure?

Ultimately this calculation is just a measure of the amount of data the format is serving over time. Different pieces of software measure data rates with different units, so keeping track of it all can be somewhat confusing.

Delivery codecs

This kind of procedure only makes sense for delivery codecs like H.264, HEVC, AV1, etc., which allow different data rates to be set.

The math isn’t difficult

Let’s say you have a 1080p video file that’s 14 minutes and 23 seconds long, and you get a request for the output to be no more than 800 MB.

To preserve as much video quality as possible, you want to make the file as large as possible without exceeding 800 MB.

First, set up the equations to keep track of what you know you need, and what your constraints are.