previous   next   contents  

16. Requirements for a SMIL Basic Profile

Kenichi Kubota ( kuboken@Research.Panasonic.COM), Panasonic
Aaron Cohen (, Intel

Table of contents

16.1 Abstract

This document describes the requirements for a SMIL Basic profile, which is intended to meet the needs of low power devices such as mobile phones and other information appliances. It includes comments and discussion about the need for modules that only include the basic syntax and semantics of the SMIL language profile.

16.2 Introduction

16.2.1 SMIL and Modularization

The SMIL language [SMIL10][SMIL-BOSTON] includes powerful functionality for multimedia services not only on desktops but also for information appliances. SMIL content authors may wish their works to be available on a widespread variety of web clients, such as desktops, television sets, PDA's, mobile phones, car navigation systems and voice user agents. Each of these platforms has its specific capabilities and may require its own profile. The SMIL Modularization draft [SMIL-MOD] provides a solution to create subsets and extensions of the full SMIL language profile, in addition to providing the means to integrate SMIL functionality into other languages.

The HTML group has demonstrated the effectiveness of modularization in working on module-based XHTML [XHTML11], [XMOD], [MODMOD]. They also shed light on the path towards greater interoperability of content among various user agents, by making the requirement that the document profile of the content act as a basis for interoperability guarantees [XHTML-PROF-REQ], by issuing guidelines for HTML content [MOBILE-GUIDE], and by providing a minimum subset for portability and conformance [XHTML-BASIC].

16.2.2 Neeed for a SMIL Basic profile

Mobile phones with web browsers have come on to the Internet providing seamless connectivity with fairly broad bandwidth, enabling multimedia services. They might become the smallest SMIL compliant devices. Internet access with mobile phones, however, has some characteristics specific to the wireless environment and its hardware and software constraints. Therefore it seems necessary for the SYMM Working Group to consider a lightweight SMIL profile for mobile phones and to provide a basis for interoperability guarantees between the cutting-edge full SMIL profile and the mobile profile.

The CC/PP [CC/PP] mechanism provides a way to notify device capabilities and user preferences to an origin server and/or intermediaries such as a gateway or proxy, that allows us to generate or select or transform tailored contents. Thus CC/PP can be used with transformation of available documents between client and server. However, as for clients, it is unclear which kind of profile they should support?

Content authors wish their SMIL documents to be delivered to as wide an audience as possible. Client users expect to enjoy SMIL presentations with various kinds of devices, which may have different profiles. Therefore, some consensus between these profiles is useful. The SMIL Basic profile would provide that minimal profile.

"XHTML Document Profile Requirements" [XHTML-PROF-REQ] describes a framework for content negotiation, and requirements for document profiles from the viewpoint of content developers and designers of different kinds of web user agents.

The SMIL Basic profile would consist of a reduced set of modules among the variety of SMIL modules in terms of semantics and syntax, and assures conformance by using a subset of the full SMIL specification. It also describes appropriate behavior of a conforming user agent. A profile for mobile devices can be tailored according to SMIL Basic profile with or without extensions for mobile specific features, and entitled "SMIL Basic". The SMIL Basic profile will provide the same benefits for other devices such as PDA's and TV sets. It should serve as a means of providing SMIL across a wide range of mobile and, further, personal electronic devices.

The Basic Profile does not propose to restrict extension, but aims at a baseline of conformance between the full SMIL and one appropriate for mobile services.

16.3 Requirements for SMIL Basic Profile

16.3.1 Target Devices

SMIL Basic profile must be a client profile which can be supported by wide variety of SMIL players, even those running on small mobile phones. Mobile devices share some common characteristics:

  1. Small display, Display can render texts, images, audio and stream data in a small area.
  2. Simple input method, Input devices are numeric keys, 4-way arrow keys, and a select key. Some may have a pointing cursor. A few may have a voice interpreter.
  3. Real-time embedded OS, Resources for calculation is limited by priority order of each task. So, in a SMIL player, the use of timers should be restricted in number and frequency, and memory should be used sparingly.
  4. Wireless network transaction, Network transactions should be reduced as much as possible.

@@ This is written to promote reader's understanding of mobile environment.

The following media could be supported:

This section states requirements for the SMIL Basic profile starting from these points.

16.3.2 Generic requirements

The generic requirements to be considered are that the SMIL Basic profile should:

  1. Consist of a comfortably small set of modules chosen from the full set of SMIL modules in terms of required semantics and syntax.
  2. Assure conformance to the cutting edge SMIL.
  3. Describe appropriate behavior for a conforming user agent according to SMIL syntax and semantics.

16.3.3 User Interface

On a SMIL player window, the user would handle arrow keys to move focus on objects and anchors, and select the target which activates playback or linking. A pointing cursor "mouse-like" device might not be supported. So "move focus and select" is a simple user interface for communication with the SMIL player.


@@These suggestions are not a complete solution however.

16.3.4 Timing and Synchronization

SMIL Timing and Synchronization presents dynamic and interactive multimedia according to a timeline. The SMIL timing model is expressed in a structured language effectively. The timeline normally needs to be calculated with limited resources of memory and the processor. For example, recursive function calls, caused by nesting elements, or memory allocation, say by additional timelines, at any moment should be restricted. The timeline should be a simple and single sequence of media objects. To achieve these, the single time container (use of par or seq) and single timing attribute value may be preferable. In a list of timing attribute values, events can be activated with "click" and also with numeric keys familiar in phones or TV controllers. For the simplest documents, if timing of "begin", "dur", or "end" is not specified, discrete media in a time container should be allowed to be shown if the region related with each of them has only one object of each, that means, "fill=freeze" is default even when unspecified.


16.3.5 Layout

Layout Module presents spatial layout related with objects in a screen. Presentation on a small display has some difficulty in rendering objects. Layout of objects may not be adjusted flexibly comparing their specified regions. So, the layout should be simple and effective.


@@ This last does not seem lightweight.

16.3.6 Media Object

Media Object Module presents description of media which constitute contents, such as text, image, audio and video.


16.3.7 Linking

Linking Module presents a hyperlink to relate objects with contents on a request by users. "a" and "area" links could be activated with focus and selection control and also with "accesskey". These linking elements might also be within single time container.


16.3.8 Structure

Structure module describes a structure of SMIL Basic documents.


16.4 Use of SMIL Basic Profile

SMIL Basic profile, can be used as is, is intended to be appropriate for small information appliances like mobile phones, and PDAs. Its simple design could serve as a baseline profile for extension for specific purpose. As for HTML+SMIL, another use of SMIL Basic may be to integrate SMIL Basic timing and media functionality with the HTML mobile profile.

previous   next   contents