Windows video. (Hardware Clinic) (Column)
by Mark Minasi
Windows video has arrived, along with a Pandora's box of troubles--and a diplomat's pouch of compromises.
This month, I'm reporting on my experience with the new Video for Windows capture boards and recording software.
Since January I've worked with the Creative Labs Video Spigot (which has been acquired by Creative Labs), and the Intel Indeo. Of the three, I like the Spigot best. As I explain how all this works, you'll see why.
PC video is playing catchup with Macintosh video. Acouple of years back, Apple introduced a technology called QuickTime, which allows you to record and play movies on your Mac. The images are small--most QuickTime movies run in a window about 160 pixels by 100 pixels.
Many video capture boards can capture 640- x 200-pixel videos, but the recommended size (and the default on some of these systems) is 160 x 100.
If you need to be able to capture video at 320 x 200 or greater size, you'll pay a price in processor speed. One of the fastest video capture boards, the Intel Indeo, can handle no more than 320- x 200-pixel capture when it's placed in a 66-MHz DX2 computer. The same goes for the Spigot when it's installed in a 50-MHz DX.
Is 320 x 200 good enough? it's betterthan 160 x 100. But there's a significant trade-off between the size of each screen and the number of screens captured per second. At 160 x 100 pixels, the boards can capture up to 25 screens per second. At 320 x 200 pixels, the speed drops to about 15 screens per second. To perceive a series of still pictures as smooth action, the human eye needs to see them at a rate of at least 32 screens per second.
At higher resolutions, the problem becomes even more bothersome. I've tried capturing 640 x 480 screens, but even at speeds at low as five screens per second, the boards couldn't keep up.
Despite its problems, animation at 320 x 200 is good enough to serve as an accompaniment to a stored voice message. The files store both voice and video; their extension is AVI (Audio/Vido Interleaved).
Although Windows video is admittedly and early technology, that doesn't mean you should ignore it. I've found it useful for producing digital still pictures. I delivrer technical seminars on PC troubleshooting, support, and maintenance. I develop course books filled with adice, warnings, and anecodtes. For years the books have lacked photographs. My staff includes people with excellent drawing skills, and drawings often get the point across, but sometimes nothing but a photograph will do.
You'll get heartburn if you try to create videos with these capture boards, but you can easily make color stills with almost all of them--and that's why I've come to love the.
I recently ripped the hard disk section out one of my course books and replaced it with a how-to section on SCSI. Anyone who's used SCSI knows that one of the most annoying things about it is the profusion of cable types in the SCSI world. Believe it or not, you hook up two SCSI devices with any one of four different kinds of cables, depending on what the maker of the SCSI peripheral felt like using. Most SCSI host adapter boards have connectors for two of those cable types. Before you venture to link together a daisychain of SCSI peripherals, you should know what connectors to look for. What's the best way to include pictures of the cable types and some common adapters? Digital stills.
Using a regular video camcorder, I walked around my office, borrowing cables and shooting them from different camera angles. Then I hooked up the camcorder to the video capture board and replayed the tape into the PC.
When I found shots that I liked, I just clicked on the Capture Single Frame option. Instantly, I had a 24-bit BMP image of the cable. When an image wasn't quite clear enough, I enhanced it using Gray F/X, a terrific image enhancer (with, unfortunately, one of the worst user interfaces in the world). Then I used Paint Shop Pro, probably the best shareware image processor for Windows, to convert the image to grat scale, popped the image into my document, and voila! Instant illustration. This, by the way, is one reason that I don't like the Intel Indeo board. It won't do single-frame captures without some fiddling around. Both the Spigot and the Blaster will do single-frame captures without any trouble.
Here's what you will need to get started with image capture.
* A Windows-capable machine of at least 25-MHz speed (486 preferred)
* RAM of 8MB-12MB for most capture boards (16MB is actually bad for most capture boards--see below)
* At least a 256-color capability for video under Windows, 16-million-color (24-bit) capability preferred
* Plenty of available hard disk space for capture
* A video capture board
* Some source of VHS or Super VHS video signals (either a VCR or a camcorder)
* A Windows-compatible sound board (optional)
It's a hefty list, but it's not as bad as it looks. Let's start with the PC. It should have a fair amount of CPU horsepower because of the volume of data running through it. You can use a 386, but this is one case where having a 486 will really pay off in speed of execution.
You'll need a video board capable of working with a lot of colors, or at least a lot of grays. The number of colors you'll see is determined by your video board and the kind of video driver you use. Drivers for 256 colors are common these days, so if you've got Super VGA, use the 256-color drivers.
Screen resolutions above VGA's 640 x 480 are not necessary, and they'll slow down the capture process unnecessarily, so use 640 x 480 with 256 colors as your video mode when working with video capture. The next step up for many video boards is a 16-million-color (24-bit) mode. You can live without a 24-bit mode, but there will be times when you'd like to have it, so keep the drivers around (if your board can use them). You won't use the 24-bit mode most of the time because, as you'd expect, it slows processing speed. Under no circumstances should you try to do Windows video capture with a 16-color board.
For the best video speed, look for a video accelerator--one that interfaces via local bus, if possible. Although video speed is important, it seems that no video is fast enough to satisfy the Microsoft Video for Windows program. Every time you start it up with a new video driver, it runs a speed benchmark on the video board and always finds it lacking. Even what may be the fastest Windows video available (an ATI VLB Mach 32) was deemed too slow for Video for Windows. I have concluded that there's just no satisfying this program.
When you buy a disk drive for use with Windows video, buy more than you think you'll need. I once recordded ten minutes of normal VHS video, only to find that it took up 160MB of disk space. Not everything is going to take up that much space, but 3.75MB for each second of recording will convince you to keep your videos brief.
Now that I've told you to buy the most computer that you can lay your hands on, you might expect that I would proceed to recommend lots and lots of RAM, but surprisingly, many video capture boards will not work if you have 16MB or more.
Most video boards are overlay boards. They contain 1MB of RAM, which is used to store data, and they must share that 1MB with the CPU. It's the primary vehicle for communication between video capture boards and the CPU. This megabyte of RAM must sit somewhere in the memory address range below the 16MB mark.
Most 386DX and 486DX clones only offer memory expansion options of 4MB, 8MB, 16MB, 20MB (possibly), and 32MB. But if your machine has 16MB or more of RAM, there isn't any room for the megabyte on the video capture board. As a result, you're limited to 8MB as a maximum amount of memory. True, some major-brand computers offer 12MB because of their proprietary memory structures, but that's not a heck of a lot better than 8MB. It's ironic that you need a Windows Ferrari in order to do video capture, but when it comes to RAM, you're a pedestrian.
This memory debacle is another reason to love the Spigot. It doesn't have one of those silly memory buffers. All it needs is an 8K area that fits somewhere between 640K and 1024K, which is child's play to configure (at least when you compare it to the other alternatives). The Indeo has similar requirements, but it seems to have some undocumented use of memory that causes it to conflict with other boards; I've spent many an afternoon laboring to make my Intel Indeo board work with my Intel Express 32 Ethernet card.
Once you've got the right machine, you need the right input signals. Most video boards will accept either VHS or Super VHS signals as input. A Super VHS source is a better choice, as it provides higher-quality input--or does it? As it turns out, the question of improved resolution is relevant only on tape playback. if you're piping the camera's output straight into the capture board, it doesn't matter whether you've got an 8-mm, VHS, or Super VHS camera. An inexpensive VHS camera will do as will for direct input as a more expensive camera. So, you can save some money on your input device.
A much better way to spend your money would be to acquire a VCR with an above-average pause capability. That makes it easier to extract a single frame from a sequence. Although capture boards are generally able to grab single frames on the fly, it's nice to have a rock-solid picture on the screen to capture. If you don't have a good pause, you can still get a good motionless video image by putting your camera on a tripod and taking about two minutes of video of a motionless subject.