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Video Capture

Not that long ago, there was a thriving industry that took people’s old 8mm home movies and other footage and copied it onto VHS video tape. It may not surprise you to know that VHS itself may soon go the way of the dinosaur. The rising star in video capture is a format called MiniDV. As its name implies, it captures video as a digital signal rather than the analogue used by VHS, and the tapes themselves are physically smaller, about the size of an audiocassette. This means the cameras can be smaller too, almost pocket-sized in some units.

Inside, the tape is 65 meters long and can hold one hour of video, roughly 11GB of compressed data. Other than the tape, the MiniDV camera uses the same basic technology as a single-frame digital camera. A chip called a CCD (Charge-Coupled Device) captures the visual signal. Most MiniDVs have a single CCD chip, which must use 3 cells to record a single pixel of the image. That’s one cell for green, one for blue and one for red, which are then combined to create a full-colour image. The more high-end (and expensive) units have three separate CCD chips, one for each colour.

Once you have captured on tape the cutting of the kid’s birthday cake and the following food fight, what can you do with it? With many units you can cable directly to the TV, and there are also adapters that allow you to play the MiniDV tape in a VHS player. For the typical reader of this tech tip though, the real fun starts when the image can be loaded into a computer. The best option for this is a 1394 connection, also known as Firewire (or iLink if you have Sony equipment). Firewire has been familiar to Mac users for some time, and in fact Apple Computer owns the Firewire trademark, but for PC owners it will probably require an add-on PCI card.

At one time, it was common to hear Firewire described as USB on steroids. Like USB, Firewire is a hot-swappable plug-and-play connection that allows multiple devices to be daisy-chained, but the original Firewire (1394a) was many times faster than the original USB 1.1. Later Firewire was matched by USB 2.0 but now a new standard called Firewire 800 (or 1394b) has upped the stakes again. Here is how they all stack up:

There is more to it than just speed, though. Firewire supports isochronous data transfer, which is a $10 term meaning the signal is clocked and things occur at a predictable rate. It turns out this is very important when dealing with real-time video, which is one big reason why the Firewire interface dominates over USB in the video industry. And if you own a fairly recent digital video camera, it’s a good bet that it has a 1394 jack.

Firewire opens a whole new playground for amateur videographers. With VHS, the data had to be transferred to the computer sequentially, and in practice most editing was actually done during the recording. Firewire is a bi-directional interface that allows the downloading to be controlled by software on the system. It is possible to ‘scrub’, which is an industry term meaning to fast-forward and rewind through the tape, selecting clips to download. Furthermore, the recorded MiniDV signal has a time stamp embedded right on the tape, making it possible to capture these clips with an accuracy right down to the exact frame. With the right software, editing can be almost as simple as cut-and-paste.

A few years ago the breakthroughs of desktop publishing brought about a revolution in graphic arts and allowed businesses large and small to produce printed material that previously would have needed the expensive services of a professional printing company. The combination of MiniDV, Firewire, low-cost editing software and web-based multimedia promises to do the same for video, and Hollywood and Madison Avenue may never be the same.

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