John McGowan's AVI Overview: Miscellaneous Questions

PC Video Chips and Cards

The current (6/21/97) generation of graphics controllers for PC's incorporate a number of hardware features to improve playback of video, including AVI. Video acceleration features have become standard in most chips. As a consequence video chip and card marketing has increasingly emphasized 3D graphics acceleration features in an effort to differentiate chips and cards from different manufacturers. These video acceleration features include hardware color space conversion and hardware scaling of video.

Color Space Conversion

Many video standards such as Indeo, Cinepak, and MPEG operate in a luminance - chrominance color space such as YUV, YCbCr, etc. Computer monitors use RGB (Red/Green/Blue). The decoded video signals must be converted from YUV to RGB for display. Most video chips now provide dedicated hardware for this color space conversion.

Hardware Scaling

Displaying a video in a windows larger (or smaller) than the encoded aspect ratio involves duplication of pixels. Complex filtering operations can reduce or remove blocking artifacts when a video is scaled up in size. If scaling is performed in software using the PC's CPU, the scaling will absorb many CPU cycles, possibly resulting in degraded video playback depending on the speed of the CPU. Most video chips now provide dedicated hardware for scaling video.

Video Cards

PC video cards are printed circuit boards. Today (6/23/97), virtually all video cards are PCI cards, with a PCI bus connector along one side of the circuit board. The video card will have at least a DB-15 connector for the VGA cable to the computer monitor. Video cards have a chip variously known as a graphics controller, graphics accelerator, video chip, video controller, or something similar. The graphic controller is the heart and the brain of the video card. The card has one or more memory chips forming the video memory where the images are stored. The video memory is known as a framebuffer. Video cards have a RAMDAC (Random Access Memory Digital to Analog Converter) which convertes the digital image stored in the framebuffer into an analog signal for the RGB monitor. PC video cards have a ROM (Read Only Memory) with the VGA BIOS used during the PC boot process. There is also a clock that provides the timing signals for the entire board. Many video cards have a feature connector allowing an auxiliary card to be added to the main video card. The auxiliary card adds additional features such as hardware MPEG decoding. Although AVI should be independent of the video chips and cards used in a PC, there can sometimes be problems or technical issues specific to a particular chip. By far the most common PROBLEM is a subtle bug in a video chip driver or a subtle conflict between a video chip driver and another driver or piece of software on the PC. Downloading and installing the latest video driver from the chip or card maker's Web site is a frequently successful fix for these problems. ALSO, Windows 3.x and Windows 95 use different Device Drivers than Windows NT 3.51 or Windows NT 4.0 Windows 3.x and 95 use Device Drivers known as VxD's for low-level hardware access. NT uses its own device drivers. If you use a video card or other hardware on an NT machine, you need to be sure to use the NT drivers! A number of video card companies such as Diamond Multimedia and STB that buy or license the controller chips from other companies such as S3 frequently write video card/chip device drivers with additional features or better quality than the device drivers provided by the chip company. Links to video chip and video card makers follow:
ATI Technologies Diamond Multimedia STB Systems Inc. S3 Incorporated Tseng Laboratories Trident Microsystems Matrox Number Nine Cirrus Logic Rendition nVidia 3dFX 3dLabs A fairly comprehensive list of video chipsets, video cards, and miscellaneous other information may be found at: t

Video (Display) Cards with Windows NT Drivers

Unfortunately, Windows 95 and Windows NT use different device drivers for the same hardware. While Windows 95 drivers are available for the vast majority of PC hardware, Windows NT drivers are harder to come by. Video cards with NT drivers are listed below: Number Nine Revolution 3D (Windows NT 4.0 Drivers) Return to Top

How to embed an AVI file in a Microsoft Word Document?

Media Player acts as an OLE (Object Linking and Embedding) server. This means that application such as Microsoft Word that support OLE can embed a movie. With Word 6.0 (Microsoft seems to keep changing the user interface for Microsoft Word so I need to qualify which version of Microsoft Word), 1. Select Insert from the menu bar. This pulls down a long menu. 2. Select Object... from the pulldown menu. This pops up a dialog box. 3. Select the Create from File tab. 4. Select the AVI file from the file browser. 5. Select OK This inserts a link to the AVI file at the current location within the Microsoft Word document that you are editing. The first frame of the AVI file is displayed. Double click on the first frame of the AVI file to start playback. NOTE: With Word 6.0, this sequence of Word commands embeds a graphic of the first frame of the AVI file along with instructions to invoke Media Player on an external file in the Word document. The binary AVI file remains separate. Only the file specification and a graphic image of the first frame are actually inserted in the Word document. The on-line help documentation with Word 6.0 is misleading or outright false on this point. Other Windows applications that act as OLE clients will be able to do similar things with AVI files. Return to Top

AVI and Your Health (Eye Strain)

Note: This is not intended as medical advice. If you are experience visual problems, see a qualified professional. Sustained use of computers probably causes a variety of visual problems. The most common problems appear to be "burning eyes" and focusing problems. Currently, computer monitors are usually placed around two feet from the user's eyes. This is much closer than the natural resting focus distance of the eyes, which is somewhere between ten feet and infinity. Also computer monitors are much dimmer and lower contrast than natural objects which forces the eyes to work harder to focus effectively on the monitor. This is one of the reasons paper remains a more comfortable medium for reading than computer monitors. Prolonged focusing at short distances probably causes a variety of visual problems. Computer users should look away from their monitor and rest their eyes, focusing at a distance, every few minutes. Many users do this without even realizing that they are doing it. Desktop video such as AVI probably presents greater risks than traditional computer uses such as reading. With static media such as text documents or still images, when the user looks away from the monitor and looks back, nothing changes, no information is missed. There is no penalty to looking away from the monitor to rest your eyes, focus at a distance, and so forth. With video, the video will change while the user is looking away. The user misses something, perhaps a critical event. Thus, users tend not to look away from desktop video, keeping their eyes focused on the screen for long periods of time. Computer animators who work with computer video, often for long periods, have reported these problems for years. Thus, people are very unlikely to watch two hour movies on computer monitors two feet from their eyes. Digital video will likely migrate to the same location as the television, at least ten feet away. Some Resources on Computers and Your Eyes "Reducing eyestrain from video and computer monitors " by Charles Poynton IBM's Healthy Computing - Vision Page Note: Keep in mind that IBM sells computers. Return to Top

Miscellaneous Questions about AVI and Video for Windows

What is most recent version of Video for Windows? Most recent version of Video for Windows for Windows 3.1 appears to be Video for Windows 1.1e. (10/2/96)

How to import AVI files into Lightwave

Lightwave is a powerful 3D animation program from NewTek. Originally developed for the Amiga, Lightwave has been ported to Windows 95 and Windows NT. BurntPixels produces a plug-in for Lightwave 5.0 called AVILoad 2.1 that enables direct importing of AVI files into Lightwave animations. AVILoad 2.1 is available for Lightwave 5.0 for Windows 95 and NT. See the AVILoad Web site for further details. For further information on NewTek and Lightwave, see the LightWave Web site: Return to Top

© 2000 by John F. McGowan, Ph.D.