Frame motion, which is another factor to consider in your encoding formula, is the percentage of the pixels that change from one frame to another. This change can result from a person or object moving, camera effects, or post-production effects.
- People and objects moving can include someone walking past the lens, tree leaves blowing in the wind, cars driving by, or an extreme close-up of a face.
- Camera effects such as camera panning, zooming, or hand-holding result in almost 100 percent pixel change from frame to frame, which is terrible from a compression standpoint.
- Postproduction effects such as dissolves, fades, wipes, or complex video effects result in a high percentage of pixel changes from frame to frame, yielding much poorer compression results. Try to avoid these techniques altogether if you hope to keep your files sizes small. Use simple cut edits and Flash-based effects instead.
In summary, the greater the motion within your video clip, the more information the encoder has to compress. On the other hand, if your clip is relatively still (such as a talking head video), there isn’t much changing from frame to frame, making it easier to drop more frames and resulting in more efficient compression.