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Digital Video
There was a lot of interest at the Four Directions Summer Institute 1997 and 1998 in
the use of digital video. Because of this it might be a good idea to take a moment to
think about the effective use of digital video in multimedia for use by teachers and
students, and some of the issues one has to deal as one selects video capture equipment
and works with this technology.
Platform independent Aspects
The Machine: system performance, storage space, memory.
System Performance is a key factor in the use of digital video. Yes, it is possible to do
with less than the recommendations you will find here, but as with all things computing,
you can't have too much speed or too much memory, or too much storage! Doing digital video
is processor intensive. It takes a lot of machine power to create movies that are larger
than the old quarter screen default size (320X240 pixels) so go with the fastest Power PC
or Pentium class processor you can get. Digital video files are large, so you will need as
much free hard drive space as possible 1 gigabyte of free disk space is not too much.
Memory that is installed in the machine is somewhat less critical except that when you
have too little your computer relies on the hard drive to create what is called
"virtual memory" and this tends to slow your computer down. So go with at least
32 megabytes of system memory as a minimum and experiment with turning virtual memory off
to see if you get better performance.
The Movie: pixel size, frame rate titles/credits and sound
The movie that you create will probably be one of three standard sizes, quarter screen
(320 X 240 pixels) half screen (640 X 480 pixels) or full screen (Too many pixels to
count!). The default for most systems seems to be the quarter screen size, and while this
is probably OK for web based video it is not the usual size that is being used for this
application. For non-streamed or non-web based presentations the half screen size is much
preferred and for video tape output you need to use full screen. Frame rate refers to the
number of frames that are delivered per second. An accepted minimum is 30 Frames Per
Second (FPS) but this is often hard to attain. 15 frames per second is probably a more
reasonable standard as long as your sound quality is good. Remember, your user will
forgive a bit of jerky motion in your movie but he or she will not tolerate poor sound. Or
to put it another way, never annoy the ear! To make sure you comply with this rule you may
find that you have to re-record or re-mix the audio. That means that if your original
audio is of poor quality you may have to recreate the audio and add it later. Or if
possible you might find the use of narration over the video to be effective. In either
case you will need the best quality recording equipment (a video camera is not bad) and a
quiet echo-free room in which to work. Additionally you will need a sound program to edit,
and tweak the audio (Sound Edit 16 or SoundForge for example).
The Uses: multimedia presentations and web pages.
Keep in mind that the subject of this paper is specific to the use of Digital Video in
multimedia presentations and web pages not the use of computers to edit video for
mastering video tapes which is entirely different! Digital video is finding its way into
various multimedia presentations made with programs like HyperStudio, Director,
PowerPoint, and in web pages. Digital video has many potential uses in these environments
and can be effective if done properly. The key to using digital video effectively is to
use it sparingly. The initial tendency of many users is to over use digital video in their
presentations. This results in the use of digital video where a still picture would do as
well, video for the sake of video and the use of overlong video clips which can cause loss
of user interest and poor performance which manifests itself in the dropping of sound
segments and choppy video.
Some effective uses of digital video include: using the video clip to show an action or
process that can not easily be diagrammed or described; producing an emotion such as
excitement - wonder - anticipation; and to relate primarily visually oriented information
such as a dance.
When used properly digital video can add a lot to a multimedia presentation such as those
done in Director, PowerPoint, and HyperStudio. In general web based video clips need to be
smaller than those used in a multimedia presentation that is located on the local machine.
The reason for this is to reduce download time and user wait time. The exception to this
is streamed video like Macromedia's Shockwave , Progressive Networks RealVideo or
Microsoft's NetShow. These technologies allow the video to be played as it arrives meaning
that the user has to endure less annoying dead screen time. Of course streaming video
takes additional resources, special server software and bandwidth!
While we are on the subject of web pages, you might consider using the EMBED tag <EMBED
SRC="name of your movie file here"> which causes the movie to automatically
load in the page for playing. This is a more elegant presentation because otherwise when
the user selects the link associated with the movie, the browser will spawn a new blank
page or window in which to load and play the video. Allowing this to happen means a loss
of background images and links while the movie plays. Then when your movie is finished,
the user has to either extinguish the spawned window or in some other way select the
original window to return to the interface you have designed.
There is no doubt that the digital video is a great way to provide certain content through
the visual input channels of your users. Just remember to keep the download time
reasonable, the audio clean, and the movie interesting and vibrant!
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