Render previews and render and replace in Video by Zaweba

Stack enough effects on a clip and no computer will play it back smoothly at full quality. Video by Zaweba offers two ways round that. Render previews draw demanding stretches once so they play smoothly afterwards, and Render and replace bakes a clip into a new file so it stops costing anything at all.

Reading the render bar

Above the timeline, a render bar shows the state of each stretch. Green means rendered and ready to play smoothly. Red means heavy, a stretch likely to stutter. Yellow means plain, a section the computer can probably play as it is. Glance at it before you play a sequence and you will know where trouble is likely.

Render previews

From the Playback menu, render previews draw the stretches once at preview size and keep the result. After that, those parts play from the rendered preview rather than being worked out live. Red stretches are the obvious candidates: a section with a grade, a few effects and a title will usually benefit.

Previews are made at preview size, which keeps them quick to draw. They are there to help you watch and judge the edit, not to become part of the export, so they do not lock you into anything. Change a clip and its preview goes out of date, and the bar shows it needs drawing again.

A good rhythm is to edit freely, then render previews when you want to sit back and watch a section properly, for example before showing it to someone.

Render and replace

Clip > Render and replace goes further. It renders a picture clip, with whatever is applied to it, into a ProRes 4444 file with transparency, and puts that file in the clip's place. The clip now plays as plain footage, which takes the load off playback for good.

The transparency matters. A title or graphic clip with see-through areas keeps them after rendering, so it still sits correctly over the tracks below.

If you need to change the original settings later, Clip > Restore unrendered undoes it and brings back the clip as it was, with its effects editable again.

Which to use

Use render previews while an edit is still moving. They are light, temporary and redrawn when needed. Use Render and replace for clips you have finished with that are still dragging playback down, such as a heavy graphic or a clip with a long chain of effects that is not going to change again.

Keep an eye on disk space. ProRes 4444 files are large, so rendering many clips this way fills a drive quickly. Your preferences let you choose scratch disks for previews and working files, so point them at a drive with room to spare.

Before you reach for either

Sometimes the simpler fix is the preview quality setting in the Playback menu. Dropping to Half or Quarter often makes a heavy timeline play well enough to judge timing, with no rendering at all. Save rendering for when you need to see the shot at its proper quality. Between these options, Video by Zaweba lets almost any machine keep up with a demanding edit.