The three leading architectures are:

Windows Media Player
Windows Media Player is Microsoft's streaming media architecture who have bundled a version of the Windows Media server with Windows NT Server which makes Windows Media architecture widely accessible to the Corporate world. Windows Media only supports one audio track, so it cannot play different versions for different connections. When used with an HTTP server Windows Media does not offer any scalability options, resulting in progressive download.
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Quicktime Player
Quicktime provides a number of benefits that make it an excellent choice:

Cross-platform delivery - QuickTime titles play well on both Windows and MacOS. Quicktime 3.0 version+ brings parity to both Mac and Windows. QuickTime 5 was downloaded over 100 million times by both Windows and Mac customers in its first year. Every day, more than 300,000 people download QuickTime to view news, entertainment, movie trailers and virtual reality content on the Internet. This huge user base is equipped to view your coolest QuickTime content.

Streamlined development - The fact that QuickTime covers the entire production process, from capture through editing to final playback, streamlines title development.

Wide range of application - QuickTime is a standard in broadcast, CD-ROM, presentations, and the Internet. Thousands of enhanced CDs from today's most popular artists depend on QuickTime to deliver their multimedia experiences. Tens of thousands of software titles, including some of the most popular games and educational CD-ROMs in the marketplace, use QuickTime to help deliver their content.

Wide range of available tools - Wide range of media supported: video, audio, stills, text, MIDI, 3D, VR (objects and panoramas) today.

Wide range of codecs available - This powerful application provides an abundance of media authoring capabilities. From simple slide shows to complex video and audio encoding, and assembly of hundreds of different media types into one movie file.
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Real Player
RealMedia is a network oriented, streaming media architecture developed by RealNetworks.

It offers both "true streaming" and "progressive download" delivery. It also offers scalability through its SureStream features which allows you to create up to six versions of your audio and video tracks which are specifically encoded for common user connections, and can repeatedly switch between version to deliver the highest quality stream that the viewer's connection can support at any given time, effectively handling changing network conditions, such as congestion. It is less suitable for CD-ROM and DVD.
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Real Media