MPEG-4: The Interactive Revolution - Page 4

MPEG-4 boasts of highly efficient compression techniques for both video and audio. MPEG-4’s Advanced Audio Coding codec for example, offers much better quality and smaller file sizes compared to the very popular mp3. The scheme used to transport the content is just as efficient while at the same time being highly versatile. All content is conveyed in elementary streams (ES), and any object may require one or more elementary streams. The standard further defines object descriptors (OD) to keep track of which elementary streams belong to each object.

An object descriptor keeps a list of elementary stream descriptors, which in turn link elementary streams with an object. Elementary stream descriptors can also be used to describe the type of media decoder required to render the object, configuration information used by the synchronisation layer, intellectual property information and quality of service (QoS) requirements.

Synchronisation is also another consideration and is achieved by time stamping the streams. This is especially important in cases where real time operation is necessary. Here, a constant end-to-end delay time must be established and data streams must contain timing information. This timing information establishes a time base, based on the encoder’s clock to which the decoder at the receiving equipment must synchronise. Time stamps are then attached and indicate when the data must be decoded and presented.

Streams requiring similar quality of service connections are then multiplexed together using MPEG-4’s FlexMux tool, before being transported according to the standard’s Delivery Multimedia Integration Framework specification (DMIF). The DMIF provides a transparent delivery interface for the application regardless of whether the source is a remote service or on local storage media.

The Future

The MPEG-4 standard has been in circulation for a few years now, and as yet there hasn’t been a lot of action to speak of. Most of what has gone on, has taken place on the internet. Apple for example, has adopted the standard in its QuickTime platform (it should be stated that MPEG-4 uses the QuickTime file format as the format for MPEG-4 video files), while IBM has released a free toolkit for generating MPEG-4 content that is Java based. IBM claims that because of this, the toolkit will run on any platform supporting Java.

If the entertainment industry does not get actively involved, it will most probably take an MP3 style revolution on the internet, to get things moving. While MPEG-4 is designed to work with almost any bandwidth, in reality it will be the spread of broadband internet connections that will allow MPEG-4 content to develop. Another very promising platform is the cell phone where data speeds are on the increase, and where both manufacturers and service providers are looking for new ways to attract customers. Of course, there must also be a regular supply of fresh content, beyond the usual array of trailers that are currently used for demos.

Certainly, the entertainment industry’s low profile may be justified, quite possibly fearing a spillover of piracy of copyrighted material from mp3 into visual content. If MPEG-4 is to make its mark though, it will have to do so soon, otherwise it may end up being dissected, with only bits and pieces being used, such as its mp4 file format for highly compressed video. But this of course defeats the purpose of the standard in the first place, which was to integrate all these various technologies and provide enhanced interactivity to all levels of users.