How to handle video files that eat up space on your computer
By Kim Komando
Gannett News Service
Working with video on a personal computer can be especially challenging because of its storage requirements.
A single frame of uncompressed DVD-quality video without sound gobbles up about one megabyte of storage space. Video is shown at 30 frames per second. This means it takes 30 MB of storage space for one second of video. So if your wedding video runs 30 minutes, you'll need at least 54 gigabytes of storage space, more than you might have on your computer.
For this reason, digitized video is compressed, a process that discards as much information as possible without noticeably affecting the quality.
Some compression processes reduce the resolution of the picture. This in turn reduces the amount of data required per second, but it can reduce the overall picture quality.
Compression also looks at various elements that are repeated in a video, such as colors. It indexes colors, for example, and replaces them with a code. When the file is played, the decoder restores the colors without noticeably affecting the color.
When a video is captured by a computer, the compression is done automatically. You are able to tweak the settings, but it's best to choose the default settings at first. A video may be recompressed again when it is exported, say to a DVD.
There are a number of video compression formats. These include AVI (Audio Video Interleaved), MOV (QuickTime Movie), MPEG (Motion Picture Experts Group) and WMV (Windows Media Video).
AVI is the oldest form of digital video for Windows. AVI videos tend to be large. It's best to use this format when you are archiving video, not manipulating or editing it.
QuickTime (www.apple.com/quicktime) is a format developed by Apple, but it works with both Macs and Windows. This is best used if you want to stream files over the Web. It is able to compress video enough to stream well without losing much quality.
The MPEG format (www.mpeg.org) is actually a family of standards used to compress video and audio. MPEG-1 was designed to shrink those huge AVI files. MPEG-2 is a different compression scheme that allows for higher quality of video playback. MPEG-4 is designed primarily for streaming content over the Web.
Windows Media Video (windowsmedia.microsoft.com), which largely has replaced AVI on the Windows platform, provides excellent compression and high-quality results.
You can edit video captured by analog and digital camcorders. If you're using an analog camcorder, you'll need a video capture card to convert video to digital format. With a digital camcorder, your video is transferred to the computer via FireWire or Universal Serial Bus 2.0 standards.
Digital camcorders and video capture cards come with editing software. In addition, Windows XP has a free editing program called Windows Movie Maker 2. Apple gives away its iMovie software with new Macs, or you can buy it as part of the $49 iLife software suite (www.apple.com/ilife).
Because video files are so large, it makes sense to save them on DVDs, which you can do if your computer is equipped with a DVD burner.
A DVD can hold about nine hours of video if compressed at VHS-quality or about two hours compressed at DVD quality. DVDs are recorded using MPEG-2 compression.
If you have a CD burner, you can create VCDs (video compact discs) and SVCDs (super video cCompact discs.) These can be played back on your computer and most home DVD players. VCDs use MPEG-1 compression. The quality is slightly worse than a VHS cassette. An SVCD uses MPEG-2. The quality is better than a VCD but not as good as a DVD. The amount of video you can store on a VCD or SVCD depends on the compression settings you choose, but it's generally 45 minutes to an hour.
To learn more about the video compression options available to you, check the documentation that came with your video-editing software. Experiment with the options to find compression settings that work best for your output needs, whether for the Web, CD or DVD.
Reach Kim Komando at www.komando.com.
