Now consider that you want to deliver that same video to the masses, via the Internet. Storage systems are available that can hit these speeds, but they’re very expensive. In order to provide smooth playback, your hard drive would have to dump data to your computer at a sustained 27 megabytes per second (or, as an engineer would think: 216 megabits per second ). Imagine you have an uncompressed VHS-quality video file sitting on a hard drive, ready to play. The second issue is so closely related to the first that it’s really the same problem viewed from another angle. Clearly, we need some form of digital compression to reduce that file size. Do one more calculation and you’ll see that a DVD disc (at 4.5GB) can hold less than three minutes. Do a little more math, and you’ll soon discover that the new 80 gigabyte hard drive that came with your computer will only store about 50 minutes of raw, uncompressed video – and that’s before you add the audio into the equation.
This means that your typical uncompressed video might occupy 27 megabytes per second to store. Video in the United States typically plays at 30 frames per second. To imagine how much space is required, consider that a typical uncompressed still frame of video, at the quality most of us are used to viewing, requires just under one megabyte to store. Uncompressed video takes a huge amount of storage space, regardless of whether you’re storing it on a hard drive, DVD or digital tape. The first issue, file size, is especially important for video storage. If you find this confusing, don’t worry we’re going to break it down a bit more. The primary task of a codec is to reduce the size of a digital media file and thus reduce the bandwidth, or data rate, necessary to play the file. All of the members of the MPEG family of standards are codecs or CO/mpression-DEC/ompression schemes.