Guido van Rossum

Structured multimedia authoring

We present the user interface to the CMIF authoring environment for constructing and playing multimedia presentations. The CMIF authoring environment supports a rich hypermedia document model allowing structure-based composition of multimedia presentations and the specification of synchronization constraints between constituent media items. An author constructs a multimedia presentation in terms of its structure and additional synchronization constraints, from which the CMIF player derives the precise timing information for the presentation. We discuss the advantages of a structured approach to authoring multimedia, and describe the facilities in the CMIF authoring environment for supporting this approach. The authoring environment presents three main views of a multimedia presentation: the hierarchy view is used for manipulating and viewing a presentation’s hierarchical structure; the channel view is used for managing logical resources and specifying and viewing precise timing constraints; and the player for playing the presentation. We present the authoring environment in terms of a short example: constructing a walking tour of Amsterdam. CR Subject Classification (1991): [[TO BE PROVIDED]]

Links in hypermedia: the requirement for context

Taking the concept of a link from hypertext and adding to it the rich collection of information formats found in multimedia systems provides an extension to hypertext that is often called hypermedia. Unfortunately, the implicit assumptions under which hypertext links work do not extend well to time-based presentations that consist of a number of simultaneously active media items. It is not obvious where links should lead and there are no standard rules that indicate what should happen to other parts of the presentation that are active. This paper addresses the problems associated with links in hypermedia. In order to provide a solution, we introduce the notion of context for the source and the destination of a link. A context makes explicit which part of a presentation is affected when a link is followed from an anchor in the presentation. Given explicit source and destination contexts for a link, an author is able to state the desired presentation characteristics for following a link, including whether the presentation currently playing should continue playing or be replaced. We first give an intuitive description of contexts for links, then present a structure-based approach. We go on to describe the implementation of contexts in our hypermedia authoring system CMIFed.

CMIFed: a transportable hypermedia authoring system

Creating multimedia presentations can be a complex and time-consuming process. We believe that a key to reducing the authoring burden is the use of structure-based authoring tools [1], [2]. These allow the explicit manipulation of the structure of a presentation rather than the implicit manipulation of this structure via, for example, a time-line. The CMIF authoring system supports the composition of hypermedia presentations from existing media data objects. CMIF (CWI Multimedia Interchange Format) is a systemindependent representation for hypermedia presentations; CMIFed (CMIF editor) is the main tool for creating CMIF presentations [3]. CMIF presentations can contain text, images, video and audio. These are referred to as (media) data objects. The data objects are generally kept in separate files, which may use a number of standard formats (e.g. GIF, TIFF and JPEG images are all acceptable). The author can impose structure by placing data objects in a tree. Rough synchronization (presenting data objects in parallel) is obtained by marking a tree node as parallel. Fine synchronization (the specification of precise delays) can be added in the form of specific synchronization constraints. Interactivity is added to a presentation by creating hyperIinks, which can be attached to stretches of text or areas of images. The author has considerable freedom in the effect of activating a hyperlink — it may replace all or part of the current context or initiate an activity in a different context (a context can be thought of as part of the screen [4]). It is also possible to run external programs or scripts. CMIF defines (logical) “channels” to capture the essence of resources — a channel represents a particular screen area or another resource such as an audio channel. A media data object must be bound to a channel in order to be displayed or otherwise presented to the end user. The channel specifies default values for a variety of media-specific attributes such as fonts and colors. Thus, when a presentation style is changed in a channel, this change is propagated throughout the whole presentation. Channels form the key to the transportability of presentations created with CMIFed — essentially, when a presentation has channels objects. to be mapped to a new environment, ‘only the have to be mapped, not all individual media data In the video we show the basics of structure editing using the two main editing views of CMIFed: the Hierarchy View and the Channel View. The third main view, the Player, is also shown.

Authoring multimedia in the CMIF environment

textabstractWe present the user interface to the CMIF authoring environment for constructing and playing multimedia presentations. Within the environment an author constructs a presentation in terms of its structure and additional synchronization constraints, from which the actual timing information is derived. The CMIF authoring environment presents three main views of a multimedia presentation: a hierarchy view for manipulating and viewing a presentation’s hierarchical structure; a channel view for managing logical resources and specifying and viewing precise timing constraints; and a player for playing the presentation.