Choosing a bit rate mode and two-pass encoding in Video by Zaweba

Bit rate is how much data each second of video gets. More data usually means a better picture and a bigger file; less means a smaller file and, past a point, visible blocks and smearing. How an encoder spends that data matters as much as how much there is. Video by Zaweba lets you choose the approach with Export > Bit rate, for the H.264 and H.265 encoders that support it.

The four modes

Variable bit rate lets the encoder spend more data on hard scenes, such as fast movement, water or confetti, and less on easy ones like a still interview. The overall size stays near a target while the quality stays more even. It's the sensible everyday choice.

Constant bit rate spends the same amount every second, whatever is on screen. Easy scenes waste data and hard ones can starve. Its advantage is predictability: some streaming and broadcast systems want a steady rate, and they'll say so.

Constant quality aims for a level of picture quality rather than a size. The encoder uses whatever data it needs to hit that quality, so a simple video comes out small and a busy one comes out large. It's ideal when quality matters and file size is flexible, such as a master to keep.

Two-pass reads the whole video once to learn where the hard and easy parts are, then encodes it on a second pass using that knowledge. It gets the best quality for a given file size, at the cost of taking roughly twice as long.

Which to choose

For uploading to a video platform, variable bit rate at a generous target, or constant quality, works well. The platform re-encodes your upload anyway, so giving it a clean, high quality file helps.

When you have a strict size limit, say a file that must fit an email attachment or a storage cap, two-pass is the best way to get the most picture into that size.

When a system asks for a fixed rate, use constant bit rate as specified.

For an archive copy, constant quality at a high setting is simple and reliable.

H.264 and H.265

These options apply to the H.264 and H.265 encoders that support them. H.264 is the most widely compatible codec. H.265 gives smaller files at similar quality but isn't played everywhere. Video by Zaweba can use your graphics card's encoder for speed where one is available, and the bit rate modes on offer depend on the encoder being used, so not every mode appears for every encoder.

Common mistakes

Setting the bit rate too low to save space is the classic one. Fast action and fine detail fall apart first. Do a short test export of the busiest section and look at it closely before committing a long render.

Using constant bit rate when nothing requires it wastes quality. And forgetting that two-pass doubles the encode time can upset a deadline, so add it to the render queue early.

A little thought about the bit rate mode costs nothing and can make a noticeable difference to how your finished video looks once it's out in the world.