SMIL is typically a language for delivering multimedia contents on to the web. Multimedia is defined as the integration of multiple media elements into one: viz text, graphics, audio and video are coupled up together with computer’s interactive power. During the last couple of years the area of multimedia on the internet has increased explosively. This area is expected to be one of the most important on the internet .For Example, Consider an application where a video is played for 5 sec’s ,then the audio is played in parallel with the video and after 10 sec’s an image is displayed on the screen. Hence, in general there must be a way to describe synchronization between different media elements that make up a continuous multimedia presentation. This can be achieved by many formats like Java, Html, and Flash etc. One such approach is the use of SMIL language. SMIL is a simple, vendor-neutral markup language designed to let Web builders of all skill levels schedule audio, video, text, and graphics files across a timeline without having to master development tools or complex programming languages.
SMIL is:
· Powerful –
SMIL marks a significant step toward making it easy to create low bandwidth, TV-like content on the Web. It offers a new level of control over synchronized multimedia by allowing individual components of a presentation to be choreographed across a timeline in relation to each other. It also lets you control the layout, appearance, and exit time of each file.
· Flexible –
What makes SMIL different from other multimedia presentation tools is that instead of forcing each component into a single video file, the text-based SMIL file merely references each file by its URL. Since the media files exist outside of the SMIL file, they retain their individual file sizes; there's no file-size bloat to slow download times.
· Simple –
SMIL's text-based format also makes multimedia presentations easy to edit. If you want to change when an audio component within a complex presentation begins, you can just edit the SMIL file. You don't have to rebuild the entire presentation from scratch.
· Interactive –
As an application of XML, SMIL supports hyperlinks, which makes it the first Web-specific multimedia language to offer true interactivity. For example, a Web builder could create a presentation about Amelia Earhart's solo flight across the Atlantic, making areas of the route clickable so that people watching it could get statistics about specific locales.
History of SMIL:
There are two versions of SMIL viz SMIL 1.0 and SMIL 2.0 yet released. The first version SMIL 1.0 came up in June 1998 whereas the second version SMIL 2.0 was recommended in August 2001. The CD-ROM community and the Web multimedia community suggested that it would be beneficial to adopt a declarative format for expressing media synchronization on the Web as an alternative and complementary approach to scripting languages. Following a workshop in October 1996, W3C established a first working group on synchronized multimedia in March 1997. This group focused on the design of a declarative language and the work gave rise to SMIL which became a W3C recommendation in June 1998.
A second Synchronized Multimedia Working Group (SYMM) was established in February 1999. The mission of the SYMM Working Group was to continue W3C’s work on synchronized multimedia that started with SMIL 1.0 SMIL 2.0 became a W3C Recommendation on 9 August 2001.
The SMIL Overview
2.1SMIL versions
There are three versions of SMIL yet released viz SMIL 1.0, SMIL 2.0, SMIL 3.0. The goal of SMIL 3.0 was to extend the development of SMIL as a declarative XML-based timing and synchronization language, and advance the corresponding timing model. SMIL 3.0 provided much more functionality than SMIL 2.0 in following ways:
· New markup was added, for example for
· Transition effects
· animation
· author-defined windows
· improved event-handling (events can come from UI or from network)
· hierarchical layout
· Authoring adaptive content (e.g. to have the same document display on a PC and on a mobile device).
· SMIL 3.0 is defined as a set of reusable markup modules. This allows reuse of SMIL syntax and semantics in other XML-based languages, in particular those that need to represent timing and synchronization. For example:
• SMIL modules could be used to provide lightweight multimedia functionality on mobile phones
• SMIL timing, content control, and media objects could be used to coordinate broadcast and Web content in an enhanced-TV application.
• The SMIL Animation Recommendation is being used to integrate animation into W3C’s Scalable Vector Graphics language (SVG).
· SMIL 3.0 improves the accessibility features of SMIL 2.0. It allows authors to include closed audio descriptions as well as closed captions in their SMIL presentations. On the whole, SMIL 3.0 is just a development of SMIL 2.0 and works much like SMIL 2.0, though it has much more functionality and of Course some differences in notation and structure.
2.2 How SMIL Works
SMIL provides a mechanism for content applications to interface with different internet protocols such as RTSP (Real Time Streaming protocol) and HTTP (Hypertext Transfer Protocol). It enables Web developers to divide multimedia content into separate streams and files, and send them individually to an end- user’s computer. These files are then together displayed as a single multimedia stream. Each object is accessed with a url, which means that the presentation can be made of objects arriving from more than one place and that objects can be easily reused in multiple presentations. The ability to separate out static file For example: text and images from non-static media makes the multimedia content smaller. Thus it does not take so long to travel over the internet.
The SMIL documents are streamed via RTSP but the documents shown in Windows Media Player are sent through different protocols, the picture support is sent via HTTP and the continuous material like audio or video, are sent through MSBP.
It can be observed that HTTP downloads files without regard to timelines, making clips with timelines more likely to stall. Although Real Server can also use HTTP, URLs for media clips streamed by Real Server begin with rtsp://, which causes it to use Real-time Streaming Protocol (RTSP). Designed specifically for streaming, RTSP enables Real Server to adjust streaming data to keep clips playing smoothly. When two clips play side-by- side, for example, RealPlayer communicates with Real Server about each clip's progress, indicating how much data it needs to keep playback synchronized. Real Server can then adjust the data flow to compensate for changing network conditions, reducing low priority data if necessary to ensure that crucial data gets through. Communication like this is not possible through HTTP.
2.3 Implementation of SMIL
Basically SMIL is a derivative of XML. It carries with it the rules of XML as well as few of its own. This makes the language easy to read and understand. For instance, like XML, all tags must have both beginnings and endings. To create smil documents a simple text editor is sufficient. VIM (vi editor) editor is generally preferred because of its capability in syntax highlighting. The syntax is similar to HTML. Hence it is easier for non-java programmers to use SMIL.
Examples include <B>bold</B> and <I>italic</I> tags. There are however differences between SMIL and HTML
● SMIL is case-sensitive. All tags must be written in lower case.
● SMIL is XML-based, the tags have to be ended.
The SMIL Supporters
To be able to play a SMIL document there have to be some kind of player or browser that supports the SMIL format and functionality, in which the SMIL file can be played. Following are the players that support SMIL presentations
4.1 Real-Player
Real player was written by Real in 1998. Real participated in the creation of the SMIL language and released Real Player G2 . Real player supports lots of file format and can use plug-in. The main supported formats are:
· Real formats: Real Text, RealAudio, etc...
· Images: GIF, JPEG
· Audio: AU, WAV, MIDI, etc...
Real Player uses streaming to render presentations. That means that it is not necessary to wait for all the components to be loaded to display something on the screen. The presentation is read and rendered in the same Time. The player works better when calling a SMIL file given by a Real Server, Rather than from an HTTP one.
4.2 SOJA -Player
SOJA stands for SMIL Output In Java Applet. It was written by HELIO .HELIO is a French association based in Melon, France. SOJA is an applet that renders SMIL in a web page or in a separate window. It supports the following formats:
· Images: GIF, JPEG.
· Audio: AU and AUZ (AU zipped)
· Text: plain text.
SOJA does not use streaming. HELIO choose to store media before rendering them. You have to wait until each of them has properly been loaded but the presentation will never be stopped. The advantage Of SOJA Player over other players is that SOJA renders very fast.
4.3 Grins-Player
GRiNS stand for Graphical Interface for Smil. One of the features of this player is that it is excellent at finding errors in SMIL code a couple of other player’s which supports SMIL are Apple’s QuickTime player and Microsoft’s media player.
Comparison of SMIL with Other Languages
5.1 SMIL and DHTML
D-HTML was introduced as a way to introduce local time and Animation effects into static HTML Web pages. Although some of the animation primitives in SMIL 3.0 resemble the functionality of some D-HTML uses, SMIL’s scope is much broader than the local nature of D-HTML.
5.2 SMIL and FLASH
Flash is a proprietary content media type that is primarily used for small animations. SMIL 3.0 isn’t a content media type because it doesn’t define any particular type of media (such as vector or raster images, videos, text, or audio data). Instead of media content, SMIL describes media composition. A SMIL presentation can include Flash objects. In short SMIL unlike Flash doesn’t care what type of media it works with. The goal is to provide a framework to control the media used. In the big scheme of things, Flash is still an Imation format. It has wide industry acceptance by content creators and users. SMIL, in big picture is more global in nature. To SMIL, Flash is potentially just another media type to integrate with other media type. So, any true comparison is just like comparing apples with oranges.
5.3 SMIL and MPEG-4
MPEG-4 is a format for describing a media object’s content and interaction. More precisely, MPEG-4 is a family of protocols that covers a wide range of media-related concerns but not a specific solution to any one class of media presentation.
5.4 SMIL and JAVASCRIPT
For multimedia presentations JavaScript seamlessly blends audio, video, images and text into one synchronized package. These elements are packaged and sent (or streamed) as a bundle, no single element of the presentation able to be manipulated or changed without affecting the other elements. Of course, all of the separate elements are to be stored in the same physical location. Applications
Areas where smil can be used are Internet TV, education, corporate communications, product information, financial hearings, net meetings, customer support, Customer Relationship Management and advertisement business, customized presentations for disabled people. It can also be used for making an interactive T.V.
Advantages & Dis-advantages
1. The main advantage of SMIL is that, it can be directly interpreted and does not need compilation.
2. All the files in a SMIL presentation are not baked into a single file. When a need to change one media component occurs it is sufficient only to change that media part, and no need to change the SMIL file.
3. Also, with SMIL it is possible to make SMIL files in advance and make the ingoing media afterwards.
4. SMIL is of course an XML language, so you have the advantages of being to
easily create them using an XML parser.
easily create them using an XML parser.
5. There is no good graphical interface for development of SMIL code as compared to Microsoft’s FrontPage which is used for HTML editing.
6. It is not more powerful language as compared to other languages.
7. As compare to other language SMIL describes media composition.
SMIL, in big picture is more global in nature. . References
URLs:
· http://www.w3.org/TR/REC-smil/
· http://www.helio.org/products/smil/smil/tutorial/
· http://www.w3.org/AudioVideo/
· http://smw.internet.com/smil/smilhome.html/
Book Referred:
1] Fundamentals of Multimedia [page No: 12, 13]
Author: Ze- Nion Li Mark S. Drew.
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