The Preview Scaling setting may be used to reduce the resolution of video processing when you are using a fair amount of filters, transitions, and track blending. This may help with the performance during the editing process.
However, keep in mind that the source video or images must typically be scaled down to the designed preview scale, and that will have a processing cost.
The submenu lists only the vertical resolution. The horizontal resolution depends on the aspect ratio of your project.
- 360p is a good choice on a 1080p screen or less
- 540p is good choice when working on a high density screen or screen with resolution > 1080
720p is a good choice when working on a 4K screen or with 4K UHD footage and you want to get a
little more clarity
Preview Scaling was added in version 20.02.
Export > Advanced > Video has the option Use preview scaling.
This is intended to provide a faster export for draft review. You should leave the export resolution set to the project resolution unless your preset or video codec dictates a resolution.