For online editing, you edit clips at the level of quality required for the final version of the video program. This is the default method of working in Premiere Pro. Online editing works well when the speed and storage capacity of the host computer are adequate to the demands of the video formats used. For example, most modern computers can handle the data rate of DV in full resolution. They may be challenged, however, by the greater demands of, for example, HDV or HD footage. For many videographers, that’s where offline editing comes in.
In offline editing, after capturing high-resolution clips, you make low-resolution copies of them for editing purposes. After editing, you replace the low-resolution footage associated with the clips with the high-quality original footage. You can finish, render, and export your final product in high-resolution. Editing the low-resolution clips allows standard computers to edit excessively large assets, such as HDV or HD footage, without losing performance speed. It also lets editors use laptop computers to edit—for example, while on location.
You may edit a project with the high-resolution footage remaining online throughout the project. On the other hand, you may edit in a two-phase workflow. You make your initial creative decisions with the high-resolution footage offline. Then you bring the high-resolution footage back online for fine-tuning, grading, and color correction.
You can complete an offline edit of, for example, an HD project with Premiere Pro, and then export your project to EDL for transfer to an editing system with more powerful hardware. You can then perform the final online edit and rendering, at full resolution, on the more powerful hardware.