Tips & Techniques
Technique : MultimediaComputer-literate musicians are well placed to take advantage of multimedia technology. You know all about the sound – now what about the visuals? PANICOS GEORGHIADES and GABRIEL JACOBS give an introduction to desktop video on the PC.
Many would argue that today what you see in an audio-visual presentation, be it a film or a pop video, is as important as what you hear. And a new element, that of interaction is increasingly being added to the audio-visual cocktail. Peter Gabriel, on his new CD-ROM, offers you the chance to mix tracks to your own satisfaction. You can get related information, view video clips, still pictures and so on -- but you are the director of your personal entertainment. As a computer-literate musician, you could be well placed to take advantage of the multimedia revolution (you probably already have some of the necessary hardware), but you need to be able to handle motion video as well as sound in order to get in on the inter-disciplinary action which is beginning to take place – and that's where this article comes in.
Sound On Sound has been concerned in the last decade or so with what new technology, especially computers, has done for sound. So what have computers done, beyond technical achievement? They've brought sound production from the expensive specialised studio to the home. Anyone with a computer, one or two sound modules and a DAT recorder can today master a CD. We wouldn't want to suggest that the title of this magazine be changed to something like Sound on Vision, but readers should be aware that similar developments are now taking place in the world of video. Let's briefly explore this impending revolution, and see what's on offer.
WHAT'S POSSIBLE?
Working with digital video on a computer is not fundamentally different from sampling sound, or using a digital audio hard-disk editing system, except that of course you're dealing with pictures.
Video signals are initially input into a computer from a video camera, camcorder, or VCR via a board (sometimes called a card) known as a frame grabber or video capture board. These usually accept composite video or Hi- 8/S-VHS signals. They capture video frames, digitise them (convert them to numbers) and send them to the computer, which stores them to the hard disk.
Once the video is inside the computer as a stream of numbers, you can, as with sound, manipulate it in any way you want. You can carry out frame-accurate edits, change its colour information, re-size it, speed up, slow down, superimpose one scene on another, even transform images from one to another (morphing). And since you're only handling numbers, you don't have the deterioration of second generation recordings typical of analogue signals. What's more, the data is stored on a hard disk, so you have random (virtually instant) access to any part of the video. In other words, you're not dealing with sequential tape storage, and you don't need to use time-coded synchronisation units and expensive tape machines with accurate transport mechanisms. Synchronising audio to video is very easy when you're in the world of digits.
Once you have the final result, you can then play this on a computer, store it on CD-ROM, or record it back to a VCR via a VGA-to-PAL converter box (this converts computer graphics signals to video signals).
All this sounds very simple, and it is. But unlike the manipulation of digital audio data -- which is now manageable on present middle-of-the-road PCs -- digital video has limitations, even on high-powered computers. The reason for this is the amount of data involved.
Digital audio (stereo sampled at 44kHz and at 16-bit resolution) requires 176Kb per second (about 10Mb per minute) of storage space. Digital video of VHS quality (assuming 260 lines) requires about 450Kb per frame -- that's about 11Mb per second or 660Mb per minute: 66 times the amount required for high-quality sound! Furthermore, although CD-quality sound is good enough to fool our ears, VHS-quality video is not. To get the quality you see on your TV while watching a live TV broadcast (approximately 550 lines instead of the 260 of VHS) would require over 1400Mb per minute, and still that's not good enough to fool our eyes.
So, achieving the equivalent of CD audio quality in video terms is a long way away. Indeed, some predict that this will only be possible well into the next century. What is possible with present hardware is VHS-quality video (some say that it's better than VHS, but there's not that much in it). Even this level of quality is only possible with compression, but the good news is that unlike audio compression (where the state of the art is only about 4:1 on DCC and MiniDisk), video compression can be a great deal higher -- up to about 150:1. This amount of compression is what makes playback of digital video, although admittedly crude digital video, possible via a telephone line (VOD -- Video On Demand) or from a CD (Video CD using MPEG-1 -- see the Glossary).
Not surprisingly, for such high compression ratios, special hardware is needed. It's not all that expensive, but standards are still in flux so it's hard to know what to buy and when. However, even without such hardware, digital video is possible (in a window) if you have a relatively fast PC.
YOUR OWN VIDEO EDITING SYSTEM
Here we'll describe a setup and give some basic guidance for producing video clips that will play within a window. Because the quality will be (at its best), similar to VHS, domestic equipment is satisfactory for many parts of the system.
First the video equipment. This will consist of:
• A camera/camcorder.
• A VCR.
• Some video studio gear, if you're intending to film indoors.
Many of the rules relevant to recording sound apply here. As with sound, you should always aim to have your signal as good as you can at source level. And again as with sound, what goes in should always be of better quality than the quality you want at the end, both in terms of signal-to-noise ratio and resolution (detail).
If you're lucky enough to own a professional or semi-professional camera capable of 700 lines, you're well away. But most domestic camcorders give adequate quality, especially when plugged directly into the video grabber board. Good domestic camcorders give about 550 lines, as opposed to the 700-plus lines of professional units. However, resolution is no great problem, since the resulting video will play in a small window and will not be more than 320 x 240 pixels (in fact, the standard for a 33MHz machine and no extra hardware for decompression is only 160 x 120 pixels -- again, see below for more on pixels). For recording the signal, domestic VHS recorders give about 260 lines, while S-VHS and Hi-8 equipment manage over 400 lines. [NOTE: all the figures refering to line resolutions mentioned so far are approximate, and ther vary depending on equipment models]
If you record to tape first, we recommend that you use the high-band format (S-VHS or Hi8 as opposed to VHS or Video8) if you can afford it. You're certainly better off spending any extra money on a VCR/camcorder capable of these formats rather than one with lots of gimmicks.
What has proved to be more important than resolution in digitising video, however, is signal to noise ratio. Because video compression techniques don't usually store complete frames, but only the differences between subsequent frames (the technique is known as frame difference), noise becomes a very important factor. Why? Because the computer considers it to be information, and the result is larger data files. For this reason, it's preferable to digitise straight from a camera into a video grabber rather than recording to tape and digitising later. However, this is only practicable when capturing indoor scenes, which brings us to another very important aspect of video -- lighting. This is as important to video as acoustics and monitoring are to music.
The most important distinction in the area of lighting is that between direct light and diffused light (light coming from different angles so as not to create hard shadows). Undeniably, the best lighting, especially if you're using domestic equipment, is natural light. And as any photography buff will tell you, this is better when the sun lies low -- at the beginning and end of the day.
The use of reflectors (such as ordinary kitchen foil) can help diffuse light. But for a lot of filming indoors, proper video lights are virtually a must. If you can't afford them, note that ordinary tungsten-based light bulbs give an orange tint. Fluorescent light is better, but the closest to white is that produced by halogen tubes (used in floodlights (security and garden lights).The trick is to use more than one light positioned strategically to avoid hard shadows. Of course, if you want to create special effects with light, other rules apply, including the use of filters and so on.
As for filming technique, it's advisable to use a tripod, or at least to place the camera on a flat surface rather than hold it in your hands -- unless, of course, you're after a certain effect, such as that of so-called 'cinema-verite' (though if you can remember that, you're probably too old to hold a camera steady anyway!). It's usually best to avoid using the automatic zoom function provided with most domestic camcorders -- it's noisy -- unless you have a microphone extension long enough to be far away enough from the mechanism not to pick up the sound.
These are the very basics of video capture. If you're inexperienced, it's something you'll need to study further, and -- particularly -- to experiment a great deal with.
VIDEO GRABBER BOARDS
To digitise video signals in the PC, you need a video capture board. This is the vision equivalent of a digital audio board. It takes in a video signal frame by frame and converts it to a bitmapped computer image.
For the uninitiated, it's worth mentioning at this point that computer graphics screens are maps of small squares called pixels -- each one coloured according to the information it represents. The usual colour configurations (numbers of colours that can be displayed) on a PC are two, 16, 256, 32,000 and 16 million. The latter is known as 24-bit, or true colour. It's called true colour because the human eye can resolve around two million different colour shades, and 24-bit images are therefore well above this limit.
Working in true colour gives professional results, but it requires more memory and it's slower because more information is being handled. The standard at the moment is 256 colours (8-bit). But here we're talking of the result -- you may need to do some initial capture and editing in 24-bit colour, and then convert down.
The most expensive boards will grab a full TV frame at true colour in real time, and then enable you to re-size it and convert its colour information. Some of the cheaper boards, however, convert the colour information and picture size down during the digitisation stage, thus giving less flexibility.
Video grabbers are limited to a maximum vertical resolution of 575 lines -- the visible number of lines out of the 625 used by the PAL TV broadcast standard (we use PAL, the French use SECAM, and the Americans use NTSC). However, most frame grabbers manage only 512 pixels vertical resolution, not the maximum of 575 of a PAL image. Some don't even manage that, opting instead for 480 (of the 640 x 480 VGA standard), so in effect you don't grab the complete TV picture but only about four fifths of it.
Video grabbers are often called frame grabbers because they allow you to freeze a video signal -- just as you would use the Pause button on an ordinary video cassette recorder, but without the usual interference -- then capture that frame as a single image. The facility is obviously useful for grabbing stills, but it's not of great importance in the context of desktop video.
There are many types and combinations of video grabbers. At the very low end of the market there are boards that will grab and digitise a frame in real time, but which are incapable of displaying real-time video in a window – so this type is good for desktop publishing but not for desktop video. At the middle and higher end of the market, there are boards that will display live video in a window (within Microsoft Windows) and even combine video with computer graphics. These will grab video. You can also get boards which offer combinations of a video grabber and other pieces of hardware such as a graphics card, a TV tuner and/or a teletext decoder.
GETTING UP AND RUNNING
Video grabber cards normally fit in an empty slot inside the PC, preferably next to the existing graphics card. A number of them need to be connected to the graphics card's feature connector (via a supplied cable). Obviously, this means you have to have a graphics card with a feature connector! Most graphics cards have one, but some don't, especially graphics facilities built into the motherboard (the main processing unit) -- so that's the first thing to check on your PC.
Apart from grabbing and digitising video onto the hard disk, video capture boards can overlay video (combine incoming video with that generated by the PC). Video signals are input into the video grabber board from a camera or a VCR, combined with video signals coming from the computer VGA graphics card, then output to the computer monitor.
As for software, some boards come bundled with third-party extra image-processing and presentation programs, but all boards come with utilities to control the display of video in a window, and to grab frames and save them as digitised images. To enable you to grab video, the board should provide Video for Windows Capture drivers; you need to install these in the Drivers section of the Windows 3.1 Control Panel. Usually the installation software does this for you automatically. Some also have toolkits allowing you to access the board's facilities from your own programs.
The window options can include sizeable or full screen, fixed aspect ratio or a squashable image, brightness, contrast, colour saturation, hue, RGB (Red Green Blue) values, and so on. Some software, such as that available on the Screen Machine board (see below), offer extras such as noise filter facilities, or options for grabbing either odd/even or both sets of lines in an interlaced frame.
It's worth noting that most of the boards available make use of 1 or 2Mb of physical extended memory, which means you can't have 16Mb (or more) of RAM in your PC -- the maximum you can use is 15Mb. Some boards will work with 16Mb of RAM, but use a lower transfer rate that will result in a lower frame rate capture. So you should check carefully before you buy that everything will work with your existing equipment.
And if all that technical stuff means nothing to you, get your dealer to install the board, and don't pay till you see it working properly!
We've looked at many of these boards over the years, and new models keep cropping up all the time -- especially with the boom of multimedia peripherals that has been going on over the last year. Some of the most impressive ones are Media Pro Plus, Video Blaster and Screen Machine.
SOME OF THE BEST
Rombo's Media Pro Plus is one of the cheapest and smallest boards, and it's manufactured in the UK. It comes bundled with a free pair of speakers and headphones (cheap ones... but free). It boasts an S-VHS input as well as an ordinary composite video input (software switchable), and can perform colour key masking (replacing a screen colour with the video source) and other digital effects.
Another good option is Video Blaster from Creative Labs (who manufacture the Sound Blaster digital audio boards which have become the de facto standard). The Video Blaster offers the best collection of bundled software, but has no S-VHS input. It can, however, accept input from three sources (software switchable.)
A useful feature on the Video Blaster (and on others) is the colour key option, where the video image replaces one of the screen colours. The board is designed to work with 640 x 480 displays, even though it has a video frame buffer which can hold images of up to 1024 x 512 resolution.
At the top of the cheaper range of boards is Fast's Screen Machine II. This has been around quite a while and is now in its second version. It offers three inputs (two can be used together to give S-VHS). It's also the most comprehensive of the three mentioned here, supporting VGA resolutions up to 800 x 600 non-interlaced and 1024 x 768 interlaced. It also has one of the cleanest signals we've seen, using circuits to eliminate noise, and including a time-base corrector for steadying the image and eliminating the effects of dropout frames.
Intel's Smart Video Recorder has a built-in compression chip (Indeo i750) that compresses the captured frames before storing them to the hard disk. This enables the card to capture at higher frame rates and image sizes than other cards.
VideoLogic's Captivator at £289 is also a good buy. It has a custom-designed chipset and achieves good-quality output and high frame rates without compression. You also get Video for Windows free and a CD-ROM with sample videos.
[NOTE: Video Grabber Cards do not usually capture (digitise) sound. For this you need an ordinary PC sound card. Any one with Windows drivers will do.]
VIDEO CAPTURE SOFTWARE
Digital video on the PC really took off only after the appearance of Microsoft's Video for Windows, which enables you to play back digital video off the hard disk or a CD-ROM, in a small window, without the need for any extra hardware.
And Video for Windows is still The Word in video capture software on the PC. The runtime version (for playback only) is distributed free. The full product allows you to record your own clips (if you have a video capture board and a sound board). In fact, it's now bundled with a number of video capture boards.
The package comes as a collection of programs and utilities on three disks, plus examples of video clips on CD-ROM, and includes programs for capturing and editing video and sound. The main utilities are VidCap, VidEdit and WaveEdit. Using VidCap you can capture audio and video together and save them as an uncompressed video sequence. VidEdit enables you to edit captured video clips and save them as compressed files that will run smoothly off the hard disk or a CD-ROM. You can join video clips together, add sound files recorded separately and synchronise them and so on. You can also import various video and audio formats from other programs, such as Autodesk Animator, and insert them in your clips, so you can combine animated text with video. WaveEdit is a digital audio capture and editing utility, and there are also accessories for editing and manipulating colour information.
Video for Windows uses the AVI (Audio Video Interleaved) file format. This means that the audio and video information are stored together, frame by frame as in the movies, thus both saving on memory requirements and giving fast loading and playback from any point.
When capturing video, it is up to you to select the frame size, frame rate, amount of colour information and sound resolution and sampling rate. You have the prospect of capturing 44KHz, 16-bit stereo audio and 24-bit colour, 30 frames/sec full screen movies -- if your hardware can handle it!
Video for Windows captures clips to memory, or the hard disk, in an uncompressed format, and then gives you the choice of compressing the clip in any ratio you desire, to achieve a smooth frame rate for the playback hardware you're aiming at. If it's a hard disk, that will be 300Kb per second (K/sec) or more. With a CD-ROM, it will be about 150Kb/sec (though latest models of CD-ROM drives deliver at twice that speed or more). The software specifies a 33MHz 386 with 4Mb of RAM, although we have tried slower machines with relative success.
An alternative to the Microsoft Video for Windows VidCap utility for capturing video is In-Sync's AV Recorder -- a new product to be released by the time this review is published.
By the use of code optimisation, this program results in captured frame rates about 20 to 30 per cent higher than those obtained with VidCap. Also, an audio waveform bar-line showing the envelope of the captured sound enables easier location and positioning of markers for cutting and pasting operations.
VIDEO EDITING
Video for Windows offers the VidEdit utility for cutting and pasting clips, synchronising sound, and compressing video. But if you want fancy things like wipes, transformations, superimpositions and so on, there are two other programs that do this well: Adobe's Premiere and, a new one called Razor from In-Sync.
Premiere (requiring a minimum of a 386 machine and 8Mb of RAM) enables you to mix two video tracks plus an effects track and two audio tracks. It's very well designed, very easy to use, and includes a preview function showing you what the result of your work will be before you save it. It comes with a very good selection of transitions and effects and is highly recommended.
Premiere supports Apple Mac video and audio formats (Quick Time and AIFF files). You can also use Autodesk Animator files, and you can combine computer animations with captured video. Fancy doing something like Who Framed Roger Rabbit? With this program, you can.
Razor performs similar functions to Premiere, enabling unlimited video and audio tracks to be mixed. It doesn't come with an extensive library of effects and wipes, as Premiere does, but it supports effects formats used in other PC graphics packages that you can buy separately. We've only looked at a pre-release version of Razor, and there were some program crashes; nevertheless, we're sure these will be sorted out in the finished product.
To use both these packages, you first load the various clips (audio, video and animation) into tracks on a time line. Next, you specify various effects for the joints. You then preview, and the program mixes the clips into a single AVI file. All is done using drag and drop with the mouse -- it's visual and easy.
You can create clean cuts between clips, or use transitions or overlays. A clean cut is exactly what it says. A transition uses one or more effects to join different video sections: examples are fade to black, fade from black, a curtain effect, and fade from one image to another. With a masking option, you can place an object (which can be a human being, of course) in front of virtually any type of background, as they do on TV with the weather forecast. You can also create special effects such as colour filters and greyscale.
RECORDING DIGITAL VIDEO EXTERNALLY
To record digital video from your PC to a VCR you need hardware that converts a computer graphics signal to PAL. This type of hardware comes in external or internal versions and cost from about £150 up to thousands of pounds.
The VGA Buster, another product from Rombo, at the lowest possible price but with no compromise on quality, takes a VGA signal and converts it to PAL so that you can feed it to a TV or a video recorder.
The PAL video signals available are a phono composite video, and mini S-VHS DIN, with separate chrominance (colour) and luminance (brightness) signals for better quality. There's also RGB Out instead of the computer monitor, which is the best option, provided your TV has an RGB SCART connection. The difference is like viewing Teletext in the normal way, through the decoder, when it's sharp and clear, as opposed to when it is part of a transmission, when the letters are hazy and unsteady.
To use VGA Buster, you run a TSR (resident but hidden) program, which allows you to switch between the TV and your computer display, as well as moving the image left, right, and up and down on the screen. The quality of the display is very good -- in fact, among the best we've come across -- and certainly excellent for the price. There's little flicker (only noticeable under Windows) and no noticeable colour smearing, though the final results obviously depend on the TV monitor you're using for display.
Other similar products are available from other manufacturers, costing about £300 plus. Professional versions (one is available from VideoLogic) cost about £1,500.
WHAT CAN YOU DO WITH DESKTOP VIDEO?
The technology described in this article does not deliver the high-definition or full-screen images that are required for making professional broadcast quality video productions. You won't be able to make final versions of your own pop videos for playback on MTV – unless you decide to be very artistic and use some of the technology's inadequacies (like small windows, low frame rates and image graininess) as effects.
However, given the high cost of professional video production, a very good use of what we describe here is in making demo pop videos, which you can show to record companies as suggestions before big money is spent. It would also help to test your ideas first and see whether they work; you can show the results on a PC or output them to a video tape.
Many pop videos today rely heavily on computer-generated graphics. Some of these graphics – fractals, for example – are very easy to generate, even by novice computer users, and the programs are very cheap. So you may even be able to produce some of the final material yourself.
The second obvious use of desktop video, and the one for which it was developed, is in multimedia applications: education, reference, games and entertainment. This is now a fast-growing industry, and there is demand for people with talent and experience in media such as music, sound and vision. So you may wish to get involved in this – working for a multimedia company or getting into producing multimedia applications yourself and selling them. Desktop video is very important for multimedia and is seen as the one element that was missing up until now, and which is very important for its success.
A third use is for promotional videos for companies, training videos, or in the support industry for editing home videos (weddings, parties and special occasions). Since the quality required for this sort of work is not as high as in the broadcast industry, you can use the equipment we describe here to edit final products. And with cheaper video compression/decompression boards, that handle full-screen video at VHS quality, now becoming available, this avenue offers huge possibilities.
Whatever your interests or needs are, digital video is an interesting area. The ease with which you can synchronise sounds and MIDI, and the tremendous number of visual effects that are available to you make this an intriguing medium in which to work.
THE ANALOGUE ALTERNATIVE
If you don't want to delve into digital video, there are products on the PC that will enable you to edit video in analogue form. These programs can control source and destination VCRs, or they can control the mixing of two video signals into one.
Video Director, the cheapest of these (now under £99), automates the transfer of material from one tape to another. This is something that can, of course, be done manually, but in automating the process the transitions between consecutive cuts (video clips) are made more accurate and the final result looks far more professional.
Video Director works with either two VCRs or with a camcorder and a VCR (it will work with most domestic pieces of equipment). One of these acts as the source and the other as the destination, and a cable (supplied) connects them to the PC's serial port. The computer controls the video equipment either via the infra-red remote control or via wired remote facilities (such as LANC) available on many camcorders.
The Video Director software lets you view your source tapes and define the clips you want in real time by clicking with the mouse on a Start and an End button. After defining your clips, you make up a list of those you want copied, having grouped them together, if you wish, to form scenes. They don't necessarily have to come from the same tapes. Once you have your list, you can cut and paste to get the precise order you want. After that, you leave everything to the PC, and it makes a new tape for you.
Of course, much depends on the quality of your equipment, especially the accuracy of the edits. Various options allow you to implement tools and effects such as frame advance, slow motion and reverse motion, again provided your equipment is up to the task. With professional equipment, you can edit at single-frame level, while domestic equipment will limit you to fractions of a second.
Movie Machine Pro, a new capture board from Fast Electronic, does not control VCRs, but analogue video signals. Though it's aimed at the consumer market, it can produce professional effects of the kind you see on TV. What's more, it's a board that will also capture digital video, still-frames, and video in a window, and it has an on-board multi-standard TV tuner. Its main feature is real-time video via a bundled piece of software called Movie Studio. This offers live mixing of two video signals into one, with output to a TV or a VCR. The two inputs for the mix can come from the internal tuner, or from either or both of the Video-Ins, or from a picture file stored on disk.
What can be done with such a facility? Well, for a start you can join two video clips using a transition effect (many such effects are provided). You simply move a lever icon with the mouse, or you can have the program do it automatically. Or you can use a masking technique to superimpose one video signal on another, such that parts of a foreground image can be made to become transparent, letting the background picture pass through. There's also a wide range of other effects.
VIDEO EFFECTS: MORPHING
Many effects are available with video capture boards and video editing software -- masking, posterising, and so on. But the latest craze in TV commercials and Hollywood special effects departments is showing one object transforming into another. You saw it in the film Terminator, and it's used in a number of car ads and, of course, music videos.
Just to be in vogue, you can now use this effect, thanks to a Windows program costing just £99 -- PhotoMorph. Although the present version of PhotoMorph works on stills as the source images, a new version that should be available by the time you read this will work on animated sequences.
To use PhotoMorph, you need two stills: a Start and End image. To achieve the morphing effect, you need to define corresponding married pairs of points on the two images, then specify the number of frames -- in other words, the duration of the animation. Each married pair of points represents a beginning and end location of the morphing operation.
Morphing with this program is fast and versatile (and cheap!), and its results look as professional as you can get on a PC. However, you do need to spend some time preparing your original images. You need to make sure that the backgrounds of the start and final pictures look similar. You also need to define correctly the relevant transformation points: if you're turning one face into another, matching points on the features of each face have to be defined, otherwise you won't get the results you expect to see.
No comments:
Post a Comment