About compression keyframes

Compression keyframes are different from the keyframes that you use to control track or clip properties, such as audio volume or clip rotation. When you export a movie, Adobe Premiere Elements automatically places compression keyframes at regular intervals in the movie. During compression, these keyframes are stored as complete frames. The frames between the keyframes are called intermediate frames. Adobe Premiere Elements compares each intermediate frame to the frame before it and stores only the data that is different. This process can greatly reduce file size, depending on the spacing of the keyframes. Fewer keyframes and more intermediate frames result in smaller file sizes with lower-quality images and playback. More keyframes and fewer intermediate frames result in significantly larger file sizes with higher-quality images and playback.

For example, a video of a talking person has a smaller file size than a video with lots of action, because only the mouth and tiny facial expressions change frame to frame. In contrast, a video of a sporting event requires numerous keyframes and intermediate frames, because the action changes considerably frame to frame. This results in either a larger file size or lower quality playback, depending on how much you compress the video.

Choosing compression settings is a balancing act. You need to adjust the setting depending on the type of video material, the target delivery format, and the intended audience. Often, the optimal compression setting is arrived at through trial and error.