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Just a few years ago, video was a form of creative expression intended only for tape, film, and television. However, now that broadband connections such as cable and DSL are commonplace, we're seeing a dramatic increase in the use of video on Web sites and as attachments to E-mail. The rising popularity of video brings with it a familiar challenge: Balancing the need for smaller file sizes with the desire for the best possible quality. Video compression isn't quite as straightforward as static image compression, where we can follow basic rules such as using GIF for computer images and JPG for photos. Video has many commonly used file formats, and those file formats each come with a unique and sometimes complicated set of options. In this article, we'll look at two of the the most common file formats, AVI and MPG, and look at how to select compression options when using these formats. AVI AVI stands for Audio Video Interleave. Created by Microsoft, AVI is one of the most commonly used video formats. In addition to being able to save live action video and audio in the AVI format, you can export animations from Ulead products such as GIF animator and Cool 3D as AVI files. The advantage to exporting animation in the AVI format (versus the GIF format) is that AVI can handle 16.7 million colors, and has more advanced transparency support as well. A variation of the AVI format, called DV AVI, is used to create Digital Video that can be transferred losslessly (without loss of quality) between computers and camcorders. The AVI format is dependent upon "codecs" (an acronym for compressor / decompressor). Codecs serve two purposes: They tell your computer how to encode (or compress) a video file when you save the file, and they tell your computer how to decode (or play) the file when you open the file. Since the same codec is needed to both compress the file and play the file, the choice of which codec to use is extremely important. If the codec you use to compress your file is not installed on your user's computer, your user will not be able to play the video. NOTE: Many AVI players, including Microsoft's "Windows Media Player" will attempt to download and install an appropriate codec if one is not already installed. However, you should not count on this feature, since downloads can be time consuming, and an appropriate codec cannot always be located. We'll take a look now at some commonly used compression schemes for AVI video. The screen shots for this section are from Ulead's Media Studio Pro, but you'll also be able to apply these same concepts to other programs such as Ulead's Video Studio, GIF Animator, and Cool 3D. |
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Copyright © 2000 Richard Jones
www.activeservice.co.uk |
