Compression

Once your media is in digital format, it's possible to work with it on your computer (you can learn about editing audio and video files), and even link it on a Web page. But, do you really want to require your visitors to download that 500MB file? Probably not!

Compression, or removing data from a file to make it smaller, is one method for improving the delivery of audio and video. Codecs (short for 'compression - decompression') are mathematical algorithms that decrease the amount of data needed to display audio and video, resulting in a smaller (compressed) file.

Codecs work temporally - by tracking changes from frame to frame of the file over time; or spatially - by generalizing large homogenous areas of the file instead of descibing each pixel of that area individually.

Many different codecs are available within the major multimedia architectures of Quicktime, Real/G2, MPEG, and Windows Media. We focus primarily on Real/G2 and Quicktime, because the purpose of these tutorials is to enable you to publish audio and video on the Web. Both Real and Quicktime support either true streaming or progressive download, which makes them well-suited to Web delivery.

The Real and Quicktime architectures each support their own set of codecs to optimize content such as voice, music, visual smoothness, visual sharpness. Additionally, the Real producer and Quicktime software you will use to generate the Web-ready versions of your files has simplified the task of selecting the appropriate codec. MPEG (MP3) has become very popular as a format for distributing music because of its high quality, but MPEG does generally require larger file sizes and higher processor demands.