The big names in Web-browser technology, radio companies and publishers have flocked to a real time audio technology from nine month old Progressive Networks Inc. Progressive’s RealAudio system is designed to enable users of the World Wide Web listen to an audio stream in real time, rather than having to first download an audio file. The Seattle-based company has won support from Netscape Communications Corp, Microsoft Corp, Spry Inc and Spyglass Inc, each of which will bundle they client-end technology with their Web browsers. At the same time ABC radio and National Public Radio said that they intended to make selections of their broadcasts available over the Internet. Other services providers who said they would implement RealAudio services include HotWired, Hollywood Online, Metaverse, GNN and RadioNet/Human Factor. Real Audio also enables small amounts of text to be embedded alongside the audio stream. This could be used, for example to update the on-screen score as the user listens to a football commentary. Progressive says it should be possible to embed Universal Resource Locators and use the existing hooks in Netscape and Spry browsers to force them to display particular Web pages at particular points in the audio. In order to cope with the inherent bursty nature of the Internet, RealAudio uses high compression ratio, combined with buffering at the client end. Each audio stream is compressed using a proprietary linear predictive algorithm and encoded as a fixed rate 1Kbps data stream. When audio is requested by the client, the RealAudio Server first sends data at a high rate, to fill the client’s buffer, and then throttles back the transmission rate.
Optimised for speech
Decompression takes place on the fly and consequently a personal commputer with at least a fast 80386 is needed to ensure proper playback. The company says that an entire hour of sound is compressed into 3.6Mb and at 1Kbps, and believes that the traffic will not pose a threat to the Internet. The compression algorithm has been optimised for speech, and the quality of the transmission has been described as of AM radio-type quality. The company says that the system will work fine with a 14.4Kbps modem. Progressive’s package consists of three pieces of software. The RealAudio Server will eventually be out for Windows NT and a range of Unix servers. The second piece, RealAudio Studio is being pitched at multimedia on-line creators, and includes software required to encode all the standard audio format and edit tracks. The Windows-based package will come in three forms – a trial version, available free from the company’s Web site, a standard and a professional version. Finally, the RealAudio Player client will i nitially be available as a Windows application, with a Macintosh version planned to follow next quarter. Player includes controls that enable the user to pause, and skip around within the audio stream. Beta copies of all software components can be downloaded from Progressive’s Web site at www.real-audio.com. The player software will remain free, with pricing for Studio and Server set to be announced with availability at mid-year, although Netscape, Spry et al are initially simply bundling the software with their browsers. A spokesman for Progressive said the company was working on various approaches to integrate its Player software more closely with their offerings.
