SPECIALSECTION Edward A. Fox Guest Editor Virtual Video Editing in Interactive Multimedia Applications Drawing examples from four interrelated sets of multimedia tools and applications under development at MIT, the authors examine the role of digitized video in the areas of entertainment, learning, research, and communication. Wendy E. Mackay and Glorianna Davenport Early experiments in interactive video included surro- gate travel, trainin);, electronic books, point-of-purchase sales, and arcade g;tme scenarios. Granularity, inter- ruptability, and lixrited look ahead were quickly identi- fied as generic attributes of the medium [l]. Most early applications restric:ed the user’s interaction with the video to traveling along paths predetermined by the author of the program. Recent work has favored a more constructivist approach, increasing the level of interac- tivity ‘by allowing L.sersto build, annotate, and modify their own environnlents. Tod.ay’s multitasl:ing workstations can digitize and display video in reel-time in one or more windows on the screen. Users citn quickly change their level of in- teraction from passvely watching a movie or the net- work news to activ ?ly controlling a remote camera and sending the output to colleagues at another location [g]. In this environment, video becomes an information stream, a data type that can be tagged and edited, ana- lyzed iand annotatetl. This, article explc res how principles and techniques of user-controlled video editing have been integrated into four multimed a environments. The goal of the authors is to explai I in each case how the assumptions embedded in particu1a.r applications have shaped a set of tools for building constructivist environments, and to comment on how tile evolution of a compressed digital UNIX is il trademark of AT%T 1314 Laboratories. MicroVAX is a trademark ( f Digital Equipment Corporation. PC/RT ic; a trademark of IEM. Parallax is a trademark of l’arallax, Inc. 0 1989 ACM OOOl-0782/89/0700-0802 $1.50 video data format might affect these kinds of informa- tion environments in the future. ANALOG VIDEO EDITING One of the most salient aspects of interactive video applications is the ability of the programmer or the viewer to reconfigure [lo] video playback, preferably in real time. The user must be able to order video sequences and the system must be able to remember and display them, even if they are not physically adja- cent to each other. It is useful to briefly review the process of traditional analog video editing in order to understand both its influence on computer-based video editing tools and why it is so important to provide virtual editing capabilities for interactive multimedia applications. A video professional uses one or more source video- tape decks to select a desired video shot or segment, which is then recorded onto a destination deck. The defined in and out points of this segment represent the granularity at which a movie or television program is assembled. At any given point in the process, the editor may work at the shot, sequence, or scene level. Edit controllers provide a variable speed shuttle knob that allows the editor to easily position the videotape at the right frame while concentrating on the picture or sound. Desired edits are placed into a list and refer- enced by SMPTE time code numbers, which specify a location on a videotape. A few advanced systems also offer special features such as iconic representation of shots, transcript follow, and digital sound stores. The combined technology of an analog video signal and magnetic tape presents limitations that plague edi- tors. Video editing is a very slow process, far slower 802 Communications of the .4CM ]uly 1989 Volume 3:! Number 7