Think Bigger From Filmora User Guide

Manual Render (Render Preview)

Click the Render Button to begin rendering your timeline whenever this red line appears (as when you add media or make other changes to your timeline).

The render preview window will pop up, showing the render progress and the estimated remaining time.

Once the rendering is complete, the red line will turn green.

Auto-Render

Besides manually clicking the Render Button, you can also use a feature called Background Render. If you enable it, your videos will be rendered automatically when you add your videos to the timeline for editing.

You can go to File-Preferences-Performance, set a starting time, and enable it.

By default, the render process will be performed after 5 seconds of inactivity on the timeline.

Click OK to save your settings.