Chapter 7. Designing Multimedia Presentations with SMIL and RealSystem G2
The RealSystem G2 is a completely re-engineered architecture of the RealMedia system and was built from the ground up to replace the entire line of RealAudio 5.0 encoding and streaming tools. RealNetwork's second-generation platform introduces enhanced streaming features and powerful new media capabilities that allow you to stream multiple media and datatypes, including separate audio, video, image, and text files, in a synchronized presentation. In addition, G2 offers many improvements in the efficiency and functionality of encoding and streaming media files.
RealSystem G2's SMIL-based multimedia may not have the interactive power and graphics sophistication of Flash or Shockwave presentations, but it has the advantage of a huge user base and the ease of creating multimedia with a simple markup language. By copying the SMIL tags in this chapter, you can get up and running with a fairly rich, albeit simple, multimedia presentation. In contrast, Flash packs more power and automatically takes care of complex timeline issues, but it requires learning a whole new proprietary authoring environment. Expect to see Flash used more widely for more complex high-impact presentations, such as movie and game trailers or product demos, and SMIL for more common everyday uses, such as audio slide shows, sound with scrolling text captions, and video news feeds.
The creation of streaming multimedia presentations is accomplished by using a combination of three new XML-compliant markup languages: the W3C's Synchronized Multimedia Integration Language (SMIL) and RealNetwork's RealPix and RealText. Since SMIL is an open standard, there are a wide range of applications that allow you to easily create synchronized multimedia content for RealSystem G2.
RealSystem G2 also supports an increased array of file types and formats via the RealTime Streaming Protocol (RTSP) such as JPEG, GIF, QuickTime, MPEG, MP3, MIDI, VIVO, VRML, AVI, WAV, AIF, AU, and Microsoft's ASF (Active Streaming Format). RealSystem G2 also supports other datatypes for specialty applications.
Additional key innovations in encoding and streaming include:
SureStream technology is a vastly improved method for streaming media. SureStream eliminates the breaks in media transmission due to changes in network conditions, such as a drop in throughput from 50 Kbps per second to 20 Kbps. In previous versions, the RealPlayer buffered a certain amount of data in the queue before it began to play. If the connection rate declined, the stream would still play. However, if it played the contents of the queue before the connection resumed, a break in the transmission would occur until more data was received.
G2's SureStream technology makes possible a dynamic bandwidth-detection relationship between the client and server throughout the serving process. When encoding a RealAudio or RealVideo file, the G2 encoder creates several embedded copies of the file at varying discrete data rates. The server then has the ability to dynamically switch streams based on the client's changing bandwidth conditions.
As illustrated in Figure 7-1, if a connection is initially established at 56 Kbps, and then drops to 48 Kbps, the server can detect this change and respond by altering the serving rate, at a preset increment, to accommodate the new connection speed. If the connection rate increases, it can adjust to that rate as well.
Figure 7-1. Streaming rates are tied to actual connection speeds with SureStream.
A RealAudio or RealVideo file encoded with G2 SureStream will be much larger than it would be if encoded with RealEncoder 5.0. The larger file size reflects the many embedded copies of the file that have been encoded at different bitrates. While G2 .rm files require somewhat larger storage space, they do not require extra bandwidth to stream because only one bitrate version of the file is streamed at any given time. The others simply remain on the server and are employed only if necessary, due to changes in network connections.
As a key broadcasting innovation, SureStream greatly simplifies the delivery of audio and video content to multiple bandwidth connection rates and ensures a high-quality viewing or listening experience free of drop-outs. SureStream will produce a quantum leap in streaming quality on the Web as more and more developers incorporate the G2 technology, especially those who found bandwidth negotiation with the previous RealMedia platform too complex to implement.
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