What is Digital Video?

Video is a series of images that appears as an image in motion. The first "videos" (films) were literally a series of photographs, illuminated one-by-one at a rate fast enough to trick the human eye. Digital video can be thought of as a series of images but usually the reality is more complex.

While it is possible to store videos as a series of still images (frames), this is a somewhat wasteful approach as a lot of information must be stored. Surely there must be a better way! Well, when we look at frames in a movie we quickly see that only parts of a moving image change from one frame to the next while the rest of the image stays exactly the same. If the image is of someone walking, for example, perhaps they move while the background stays the same. So why not simply describe what changes from one frame to the next, since a little description is much less information than a whole image itself?

In fact, that's what digital video does. And in a world with limited disk space and network connections, simple ideas like this one can let you store hundreds of videos on your computer, instead of a handful or download a video in minutes, instead of hours.

In addition to this technique, digital video employs other methods to reduce the amount of data in a video. Digital video often uses tricks such as describing regions of similar color instead of describing each point one at a time -similar ways are used for describing images. Or they carefully describe certain parts of the image where lots of detail or movement is happening, for instance the part you're probably staring at, while giving less attention to the boring stuff at the edges. These ideas are not new, but they are improving rapidly with exciting consequences for producers of online video.