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.
Applications that support SMIL authoring include:
- Extend Media TAG
-
As the high-end solution of choice,
TAG features all the
bells and whistles for quickly producing complex SMIL presentations
(http://www.extend.com).
- Veon VeonStudio
-
While not as powerful as TAG, VeonStudio is a complete authoring
environment for creating interactive broadband content with SMIL and
is one of the easiest authoring tools on the market. VeonStudio is
free. The VeonServer can be purchased for a small fee (http://www.veon.com).
- RealNetworks RealProducer Pro
-
Falling between TAG and VeonStudio in horsepower, RealProducer Pro
packs powerful tools for building SMIL presentations (http://www.realnetworks.com).
- Sausage SMIL Composer SuperTool
-
SMIL Composer is a freeware authoring
tool that allows you to easily add available media types, arrange
their layout and sequence, and decide how they are played in your
composition. Then, with one click, you can view your SMIL code or
preview your composition in your RealSystem G2 Player. Unlike TAG,
RealProducer Pro, and Veon, the SMIL Composer does not support the
editing of RealPix or RealText files. The tool assumes you have
RealPix and RealText files ready to go before you embed them in your
SMIL presentation (http://www.sausage.com).
- Allaire Homesite
-
This HTML editing application features a helpful SMIL tag pack for
simple SMIL authoring (http://www.allaire.com/products/homesite/).
- Macromedia Dreamweaver
-
The extensions in Dreamweaver support embedding SMIL-based RealPlayer
objects into web pages. You can download the Dreamweaver extension
free from RealMedia (http://www.dreamweaver.com).
- RealNetworks RealSlideshow
-
This free SMIL authoring tool enables consumers to compose quick
slideshows. The RealSlideshow Plus is inexpensive and packs more
interesting features (http://www.realnetworks.com).
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:
-
On-the-fly dynamic bandwidth allocation with
SureStream.
This technology automatically
adjusts data transmission rates to match fluctuations in bandwidth
conditions. If a listener's bandwidth drops off suddenly,
SureStream detects this change and sends a smaller stream to
accommodate the lower bandwidth instead of continuing to try and
shove an egg through the straw. SureStream alleviates the breaks and
pops associated with bandwidth negotiation and rebuffering in
RealSystem 5.0, which is a much needed improvement as 5.0 often
overestimates the bandwidth throughput of a user's modem.
-
Vastly improved sound quality with an 80%
increase in frequency response over the previous 20 KB 5.0
codecs. The new G2 audio
codecs are the first to be
developed in-house by RealNetworks. They reproduce higher frequencies
better than previous codecs and result in brighter, more realistic
audio. The G2 codecs take advantage of new encoding technologies and
vastly improved algorithms for compressing file sizes.
-
Simplified encoding process. In
RealSystem G2, one file serves
up to six different
connection rates. The default
bitrate settings are for 28 Kbps, 56 Kbps, single ISDN, dual ISDN,
xDSL, and T1. For the T1 setting, select whatever bitrate you want to
encode to, with the maximum at 1.2 Mbps. RealSystem 5.0 requires
encoding multiple files for bandwidth negotiation.
-
Faster encoding. The G2 encoder
offers audio encoding that is five times faster than with the
previous RealEncoder 5.0.
7.1. SureStream
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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