So, how does recording a video of your screen work? Why do videos that seem so similar have such different sizes? I wish I had a quick and simple answer to share, but capturing video is a little too complicated for that.
Video is compressed by encoding the image on the screen using key frames. A key frame is just a full image of the area being recorded; instead of taking a picture for every new frame only the differences from the previous key frame are recorded. Whenever the image changes significantly, a new key frame is generated. The final video is composed of key frames (which consist of the entire area being recorded) and transitional frames (which only show the changes from the last key frame). Key frames are larger than the transitional frames, so videos with lots of key frames take up more space than those with only a few.
I like to think of this in terms of old Chuck Jones cartoons (creator of the Road Runner and Wile E. Coyote, among others). All the backgrounds are painted and static; that takes a lot of work and having to redraw that every frame would make animation impossibly time-consuming. Because the only thing that changes in each frame is the animated character, they are drawn separately and then placed on top of the background. This is a great analogy for what happens when Jing records the screen. The big painted backgrounds are key frames and the moving animation is the stuff in-between.
What does this have to do with Jing video file size? Everything, as it turns out. Screen content comes in a few different categories. For instance, while typing this blog post there's not a whole lot changing on my screen, just the addition of a few black letters on whitespace. A recording of that would require very few key frames. Now, if I were to stop and move the window around, that would generate more key frames. The most extreme case is trying to capture full motion video playing back on my screen--this creates key frames at an extraordinarily high rate.
The codec that Jing uses to record video is optimized for the first type of activity. Jing takes lossless key frames so that the content on your screen remains easily readable. This means that Jing key frames tend to be large; a side effect of high quality video is that recordings with many key frames quickly become much larger than those with a small number of key frames.
How can you use this info to create smaller (and thus easier to share) videos:
- More movement means more key frames, so to keep key frames smaller try recording a smaller area of your screen.
- Pay attention to what’s in the background of your video. A picture of a solid color has a smaller file size than a picture with lots of variety. Changing your desktop background to one color might cut down on file size in videos where the desktop is shown.
- Think about your viewer. If they have a high speed connection, downloading a larger file might not be a big deal. If download speeds are an issue, keep your videos short and to the point; your viewers will appreciate it.
