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The predominant information forms for scholarly communication are text and still images. This seems unlikely to change in the foreseeable future. Yet, when people think about multimedia information, text and image tend to be ignored in favour of sound and video (or moving images). Print and image will be considered shortly (see 4.5.3: Page oriented solutions on page 63).What software technologies support sound and video?
In considering both of these information forms, an important initial distinction needs to made between streaming and non-streaming media. Non-streaming media require the entire file to be available before they can be played. The combination of a networked environment and a large file size can lead to long delays before the user can view/hear any of the file. Streaming media allow the user to begin to interact with them as soon as 'enough' of the file is available. What defines enough depends on the speed of the network and the file type, but can often be less than 5% of the file.
A range of non-streaming audio formats are available. In the Windows world, the WAV format predominates. On the Macintosh, any of AU, AIFF or System 7 Sound files can be encountered. These sound formats vary in whether they encode mono or stereo sound, and the audio sampling rate. Analog sound needs to be sampled to provide digital data. The higher the sampling rate, the more data is required for a given length of sound. Typical rates are 11.1 KHz, 22 KHz or 44.1 KHZ (this latter one is the sampling rate for audio CDs).
The dominant streaming audio format at present is provided by RealAudio, a product of RealNetworks. RealAudio is designed for deployment over networks and operates at speeds as low as 14.4 Kbps. The user runs a free piece of software called the RealPlayer client (available for MacOS and Windows) which communicates with a server running the RealServer software. Together, the two pieces of software communicate to stream audio data from the server to the client. The client adapts to the network speed available and allows the user to start at an arbitrary location within an audio stream, as well as to rewind, fast forward, and pause.
This software combination is routinely used to distribute audio files of all types over the Internet. One scholarly use is to archive the audio of conference sessions. An example of this is the Computers, Freedom and Privacy '96 conference held at MIT. Every session is on-line at <http://www.swiss.ai.mit.edu/~switz/cfp96/#program> for later access and replay. A particularly novel use of RealAudio has been the broadcasting of dissident Serbian radio over the Internet [Pantic, 1998].
The main non-streaming video formats are the Motion Picture Experts Group (MPEG) family of encodings, Microsoft's AVI (playable on both Windows and MacOS computers with special software) and Apple's Quicktime Movie (playable on both Windows and MacOS computers via free viewers). Of these, Quicktime is the superior format (and has just been endorsed as the basis for the new MPEG-4 encoding). The majority of video content on the Internet is encoded as Quicktime. Unless the user has a very powerful computer with graphics support in hardware, they will probably not be able to view full-screen video at 25 or 30 frames per second (fps), the standard for television or cinema. Typical workarounds are smaller than screen size windows, lower frame rates or both.
The main streaming video format is Realvideo also from RealNetworks and accessed using the same RealPlayer client. Available network bandwidth on the Internet makes accessing video on-line an exercise in frustration for most users at present. Typically the software has to drop the video frame rate to 5-10 fps just to allow the audio track to continue to play without (too much) interruption. This should improve as bandwidth improves (although modem speeds are at or near their theoretical limits and alternative technologies will be needed) and compression techniques get better (although there is just so much information that can be packed into a limited number of bits).
The Quicktime video format has just added Quicktime Quickstart which allows the user to start to play a video before it has finished its download. This is not true streaming, but it produces a similar effect.
Last modified: Monday, 18-Sep-2017 03:28:13 AEST
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