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How Much Can A DVD REALLY Hold?


DVD in a computer Some say that as we age, memory is the first thing to go. Try for a moment to recall the details of a major event in your life, such as little Billy's graduation, Jennifer's piano recital, or last month's city council meeting. Some events like karaoke at your Cousin Sandy's wedding might be best forgotten, but for the more important ones we often count on our video cameras to capture the memories.

Over time camera tapes can fade just like our memories, but thanks to the boom in do-it-yourself DVD authoring, you can now preserve every minute of the action in a high quality digital format. The first thing you might want to know is, how much can a DVD really hold?

The key to understanding the storage capacity of a DVD is to understand the fundamental difference between CDs and DVDs. Audio CDs are kind of like your grandpa in that they do things one way and one way only. An audio CD cannot hold more than 79 minutes and 59 seconds of music. DVDs on the other hand are like the hyperactive grandson who does things differently every time. The amount of video you can fit on a disc depends entirely on the quality you want.

In their original formats, both analog video (i.e. 8mm, beta, or VHS) and digital video (MiniDV, DVC, etc.) take up massive amounts of space. They contain a ton of video and audio information, each sampled thousands of times a second. Fortunately, there is a better way to fit lots of video on a fixed amount of space: it's called compression. The math gets pretty complex, but think of it like a .zip file, the data gets squeezed into a smaller file that is easier to manage. In a nutshell, compression allows you to still enjoy good quality while also cutting back on the amount of space it takes to store the video.

If you've ever used a VCR to record a television show (last episode of Seinfeld, anyone?), you probably know that VHS tapes feature a quality setting that allows longer recording times on the same tape. When taping a show, you have options like SP, LP, EP, SLP. Now these terms may sound like a bunch of alphabet soup, but they are telling you the quality at which your tape is being recorded. Slow Play tapes are higher quality, but the trade off is less recording time. On the flip side, Long Play tapes can hold much more information, but at a reduced quality. There is an inverse relationship here, can you feel it?

Now, on to the DVD recording… When we talk about digital recording we stop using terms like SP,LP, EP, SLP, and we use the term ”bit-rate.” Bitrate defines the amount of data per second being recorded. The higher the bitrate, the better the quality. Most set-top DVD recorders have some means of adjusting the video quality, or bitrate, which may be explained in the owner's manual in greater depth.

As a general rule of thumb, a DVD disc can hold about 2 hours of video at "standard" quality. If you want to retain every detail of your thirty-minute independent film project, you can get away with bumping up the quality a bit. On the other hand, if you are recording from a low quality source or if you want to preserve that old home movie feel, you can turn the quality down and perhaps squeeze four or even six hours of video on a single disc! That's enough to give everyone at the family reunion their fifteen minutes of fame, and have some space left for the three-legged race at the end!

By mastering the concept of compression, you will have much more control over the content you are putting on DVDs, whether it is home movies or church services or anything in between. You might even save some money by avoiding the need for more expensive dual-layer DVD discs when you can use compression to fit your movie onto a standard single-layer disc. Instead of asking, "How much can a DVD really hold?" a better question might be "What quality should I use so that my video can fit on a disc?" This wonderful feature of DVDs allows them to hold as much or as little as you need them to, depending on the quality of course.

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