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Chapter 2

Video Conferencing on the Apple Macintosh

The Apple Macintosh has a reputation as one of the most easy-to-use computing platforms available, as well as being one of the best suited to multimedia applications. Hence, it would seem likely that it would to be an appropriate environment for video conferencing applications. And indeed this is the case, with a number of Macintosh-based video conferencing software packages being available. In this chapter we look at the components of a video conferencing system and describe how the Apple Macintosh supports video conferencing applications.

The Components of a Video Conferencing System

Any computer-based video conferencing system, be it a stand-alone unit or one based around a desktop computer, contains of a number of important components. Firstly, there is the video camera, used to capture the image of the user. Then a digitiser, used to convert the (normally) analogue output of the camera into a digital form. Then a CODEC (Compressor/Decompressor) used to compress the digital video signal ready for transmission and to decompress incoming video data for presentation on a video/computer display. And finally there is the Network Interface and Hardware the systems front-end to the computer network that will carry the video data between the members of the video conference. The flow of data between these components is shown in Figure 2.1.

Figure 2.1. The main components of a video conferencing system.

Until fairly recently, the most significant costs of any video system have been those of the CODECs - traditionally expensive hardware devices capable of compressing a high-bandwidth analogue video signal into a lower-bandwidth digital form - and the Network Interfaces and Hardware. The high-cost of the latter being due to the fact that the computer networks used to carry digital video data over large distances have needed to be of high-bandwidth (certainly >64Kbps and often as high as 2Mbps) and hence required specialist computer equipment.

However, in recent years the price of CODECs has fallen whilst their specifications have improved. For example, it is now possible to purchase a hardware CODEC that can compress a video signal to less than the crucial 64Kbps figure for less than 2,000. The 64Kbps barrier being important because it is the bandwidth available from a single ISDN 'B' channel - the dial-up data service offered by many telecommunications service providers. Using ISDN rather than dedicated communication lines significantly reduces the running costs of a video conferencing system.

Additionally, there has been the development of software CODECs that are able to use the processor power of a desktop computer to compress and decompress digital video streams. Whilst software CODECs cannot equal the performance of their hardware counterparts (working with lower image resolutions and fewer frames of video per second), they substantially reduce the cost of creating a video conferencing system.

The Architecture of the Macintosh

The system architecture of the Macintosh allows all the main components of a video conferencing system to be integrated in a highly modular way. At the centre of this architecture is Apple's time-based data handler - QuickTime. The QuickTime extension to the MacOS operating system is now installed as standard on all Macintoshes and, amongst other things, provides video compression and decompression facilities in software (with the ability to integrate hardware 'accelerators' and CODECs) and allows video digitising boards to easily integrate with the Macintosh environment through their own 'VDIG' extensions. Additionally, the Macintosh conforms to the ISO Seven-layer networking model, allowing applications to be shielded from the underlying computer network used. The relationship between the structure of a video conferencing system and the Macintosh architecture (and in particular, QuickTime) is shown below in Figure 2.2. Clearly, this diagram is just intended to show the logical relationships between the various components involved.

Figure 2.2. Video Conferencing on the Apple Macintosh

It is worth noting that having stated that QuickTime and the Macintosh's networking architecture provide and ideal framework within which a video conferencing system can function, some Macintosh video conferencing systems (in particular the older ones) do not necessarily work in this way - with their CODECs operating independently from QuickTime and the video conferencing application interfacing directly with the networking hardware (e.g. an ISDN adapter). However, this mode of operating is rare and is likely to become increasingly more so.

Video Conferencing Systems on the Apple Macintosh

A number of video conferencing packages are available for the Apple Macintosh platform. These are listed below in Figure 2.3. and categorised in terms of the digitising board they use, whether or not the CODEC is hardware- or software-based, the type of computer network used and the approximate price. Clearly, the video conferencing market is growing rapidly and this list will no doubt be incomplete. Similarly, prices are likely to change.

Perhaps the main point to notice is that the main price difference between systems is between those that use software CODECs (and give lower frame-rates) and those that compress and decompress the video signal in hardware. Additionally, most 'high-end' video conferencing systems use dedicated video digitisers (as opposed to using 'off-the-shelf' or the AV Macintosh built-in digitisers) and ISDN communications although an increasing number will perform over high-speed modem lines (albeit at a lower frame-rate). Similarly, there is a move to the support of IP networking - allowing video conferencing packages to run over Ethernet, Token Rings and even the Internet (at, of course, much lower frame-rates!).

 
          Digitiser     CODEC     Network       Price

VidiMac Custom* H/W* ISDN* 4495 Visit Custom* H/W* ISDN* 3850 IRIS Custom* H/W* ISDN $5000 Cameo Custom* H/W* ISDN $1595 Connect Custom* H/W* Modem 3599 IP ISDN ES-F2F Spigot S/W Modem 250 AV Mac IP ISDN CU SeeMe Spigot S/W IP free AV Mac

Figure 2.3. Video Conferencing products on the Apple Macintosh


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