How proxy files keep Video by Zaweba smooth on a laptop

Editing high resolution footage asks a lot of a computer. Every time you scrub, play or jump to a frame, the editor has to decode the video, and modern camera formats are built to be small on disk rather than quick to decode. Video by Zaweba gets round this with proxy files, made automatically for every clip you import.

You never have to switch anything on. Knowing what the proxies are and how they work helps you understand why the preview behaves the way it does, and when you might want to supply your own.

What happens on import

When a clip comes into the project, the app makes a 540p proxy of it. Each proxy has a keyframe every 6 frames. Keyframes in this sense are the frames a decoder can start from without reading the frames before them, so having one every 6 frames means the preview can jump to any point in a clip and show it almost at once. Camera originals often have keyframes much further apart, which is why scrubbing them directly can feel sticky.

The sound is decoded too, to 48 kHz floating point, and the app works out the waveform peaks that draw the shape of the sound on the timeline. All of this happens in the background. You can carry on editing while it runs, and the preview gets smoother as each proxy finishes.

The result is that the preview stays smooth on a laptop, even with footage that would otherwise stutter.

Export always uses the originals

A proxy is a stand in for editing. When you export, Video by Zaweba renders from your original files, not the proxies. The 540p size never reaches the finished film, so there is no need to swap anything back or worry that the preview size will show up in the result.

This is also why your original files must still be where they were when you export. The proxies let you edit; the originals make the film.

Attaching your own proxy

Sometimes you already have a proxy. A camera might record a small file alongside each full size one, or a colleague might send you lightweight copies to start cutting before the full files arrive. In the bin's right click menu you can attach your own proxy file to a clip, and detach it again later.

The rule is that it must be the same length and the same shape as the original. A proxy that is a few frames short or has a different aspect ratio would put your edits out of step with the original, so the app insists on a match.

Attaching your own proxy is useful when the automatic one would take a long time to make, or when you have been given small files for a fast start. When the originals are ready, detach and let the app take over.

When to think about proxies

Most of the time, you will not. The background work just makes the preview pleasant. A few habits help it along. Import your footage at the start of a session so the proxies are building while you watch the material and make your first selects. Give the app a moment after a big import before you judge how smooth playback is. Keep originals on a drive that stays connected, because the export needs them.

If playback feels heavy right after importing, the proxies are probably still being made. It settles once they are done.

How it fits the rest of the app

Proxies make every other tool feel better. Trimming with the trim monitor, scrubbing a speed ramp, playing a multi-camera edit with several angles at once and watching an effect update all depend on frames arriving quickly. Video by Zaweba is fully offline, and the proxies are made on your own computer, so there is nothing to upload and no wait for a server.