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Digital Video, Part I: Compression [Newsletter: Volume 3, Issue 4]MWS Newsletter: Volume 3, Issue 4 In last month's newsletter, I talked about the reasons for the upsurge in popularity of Web Video and introduced Flash video. If you missed it, you can go to http://www.minnickweb.com/newsletter/newsletter10.html to catch up. This month, I'll be talking about compression. Compression is the process of reducing the file size of digital media. A minute of uncompressed, full-color, digital video with a frame size of 640x480 and a frame rate of 30 frames per second takes up about a gigabyte of storage space. To download such a file over the Internet would take an hour and a half over a T-1 connection or 39 hours over a 56k modem. It should be apparent from these numbers that compression is almost always necessary for any type of digital video. DVD video is generally compressed down to 250 MB per minute, but even that is way to much for the Web. The first steps usually taken to reduce the file size of video are to reduce the frame size and frame rate (number of frames per second) of the video. A video that's 320 pixels x 240 pixels will take up half as much space as one that's 640x480. After the dimensions of the video and the frame rate have been adjusted, the file can be compressed further and converted to any one of a number of formats such as Quicktime, Real Video, Flash Video, or Windows Media. Using compression technology, a Web video might be compressed down to 1/40 or less of the uncompressed video file size. There are a number of ways a digital video file can be compressed. Compression works by getting rid of the parts of the video that we can't see. For example, a typical video will contain millions of colors. Humans can only perceive a much smaller number of colors. So, by throwing away information about the colors we can't see, the file size of the video can be reduced. Further reductions are typically achieved by not storing information about parts of the video frame that don't change. For example, an object that's always in the same spot, such as a chair or a background, can be stored with much less data than an object that's constantly moving. 5 Tips for Achieving Better Compression
Next month, as promised, I will explain the different types of "streaming" video and tell you how to use streaming correctly. In the meantime: For more information about how Minnick Web Services can help you achieve your goals, please visit our web site (www.minnickweb.com) or contact us. To find out more about our digital proofing, publishing, and reporting technologies, visit the eBookHost demo at demo.ebookhost.com. ------ Complete Archives and Subscription Information Chris Minnick ------
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