There’s more to MPEG video than just compression. There are five MPEG standards – MPEG1, MPEG2, MPEG4, MPEG7, and MPEG21 – spanning all aspects of compressing, authoring, identifying, and delivering multimedia. Here’s a quick look at each one and where it fits in the digital media landscape.
MP3 is Not MPEG3
It’s the magical ability to squeeze the 1.4Mbps audio stream from a standard audio CD down to a sweet-sounding 128kbps that has made MP3 the de facto standard for digital music distribution. You can find MP3 support in every major media player on every computer platform, and dozens of consumer electronic devices can play MP3s. It’s as close to a universal format for audio as you’ll find.
MP3 is actually part of the MPEG1 standard. The audio portion of the MPEG1 spec contains three different compression schemes called layers. Of the three, Layer 3 provides the greatest audio quality and the greatest compression. At 8kbps, MP3 will sound like a phone call – intelligible, but nothing you’d ever call high-fidelity. Good-quality music starts at about 96kbps, but generally you’ll want 128 or 160kbps to get “CD quality” reproduction.
MPEG2 is Digital Television
The MPEG2 standard builds upon MPEG1 to extend it to handle the highest-quality video applications. MPEG2 is a common standard for digital video transmission at all parts of the distribution chain. Broadcast distribution equipment, digital cable head-ends, video DVDs, and satellite television all employ MPEG2; as do point-to-point streaming devices like the vBrick.
You’ll need special capture cards to encode MPEG2 in real-time on a PC. But in the streaming world, MPEG2 is a great source from which to transcode the various Real, WindowsMedia and Quicktime formats we serve to our viewers.
MPEG2 needs about 6Mbps to provide the quality you’re used to seeing on movie DVDs, although data rates up to 15Mbps are supported. 720X480 is the typical 4:3 default resolution, while 1920×1080 provides support for 16:9 high-definition television.
If you’re involved in digital media, there’s no question you’ve encountered one of the MPEG standards for video. If you’ve ever listened to music on the Web you probably used a portion of the MPEG1 standard to do it (MP3). If you use an iPod, you’re already knee-deep in MPEG4 (AAC audio). Ever watched a movie on DVD, or have DirecTV? You’re already awash in MPEG2! But wait-there’s more! The Moving Picture Experts Group – a working group of the ISO (International Organization for Standardization) – are busy folks, still working on ever more advanced standards for digital media.
The MPEG standards are all about interoperability. Generally, they are rules about how the systems and media files should interact with each other. Defining just the interfaces and behavior of the system leaves lots of room for innovation as to how things are implemented. For example, as MPEG1 technology has evolved over more than a decade, the encoders and decoders have improved – they’re more efficient, have greater compression, faster performance, better-looking video, better-sounding audio. A high-end encoder will produce better-looking video than a low-end one, even though both are producing valid MPEG1 files at the same bitrate.
The Granddaddy of ‘Em All – MPEG1
In development for years, MPEG1 became an official standard for encoding audio and video in 1992. The simplest of the MPEG standards, it describes a way to encode audio and video data streams, along with a way to decode them. MPEG1 may seem like an almost quaint spec in these days of super-codecs like WM9, RealVideo9, and MPEG4 – but don’t count it out.
You can play it on just about any computer or operating system, and it doesn’t take any special software or a lot of CPU horsepower to decode. And it’s a sure bet that in ten years, you’ll still be able to open and play those MPEG1 files in your archive.
The default size for an MPEG1 video is 352×240 at 30fps for NTSC (352×288 at 25fps for PAL sources). These were designed to give the correct 4:3 aspect ratio when displayed on the rectangular pixels of TV screens. For a computer-based viewing audience, 320×240 square pixels gives the same aspect ratio. Good up to about 1.5Mbps, MPEG1 delivers roughly VHS quality at 30 frames per second. You can scale up or down in size or bitrate, but from 1.2-1.5Mbps is the sweet spot where you’ll get the most bang for your bitrate buck.
MPEG4 – Internet Streaming and Synchronized Multimedia
Where MPEG2 was designed to scale up to broadcast and high-definition quality and operating requirements, MPEG4 goes the other way. It’s designed to scale down – down to dial-up internet bandwidths and to tiny devices like cell phones and PDAs; as well as still remain viable for high-quality desktop streaming up to 1Mbps. MPEG4’s AAC audio codec is the root of the MP4 file type, recently popularized by Apple’s iTunes, among others.
But MPEG4 is much more than just an audio and video compression/decompression scheme. It’s a container for all kinds of media objects (images, text, video, animation, interactive elements like buttons and imagemaps, etc) and a way to choreograph them into a synchronized, interactive presentation. (see Interactive Authoring for MPEG4 for more info). MPEG4 also has standard interfaces to allow plugging in a DRM scheme called Intellectual Property Management and Protection (IPMP).
MPEG4 is still at the frontier of media technologies. The specification is extensive, and each vendor implements it in their own way. Try a variety of MPEG4 tools and you’ll find lots of incompatibilities. But some are working to smooth the landscape. The Internet Streaming Media Association (ISMA) is an industry consortium dedicated to interoperability among MPEG4 products and services. Essentially, any implementation that’s ISMA-compliant will work with any other.
MPEG7 is not a video or audio coding scheme or delivery mechanism. It’s about metadata. In a world of more and more content stored in more places, the ability to identify, search, index, and publish information about content is key. Officially called the Multimedia Content Description Interface, it’s a set of rules and tools for describing content.
Most media file types already can carry a metadata payload, which is typically used for Title, Artist, and Copyright information. MPEG7 is like that…and then some. Complex and customized metadata structures can be defined using the XML-based Description Definition Language (DDL).
Metadata schemes can include descriptions of semantic elements (i.e. shapes, colors, people, objects, motion, musical notation); catalog elements (copyright and access rules, parental ratings, title, location, date, etc); or structural elements (technical stats about the media). Search engines, PVRs, live broadcasts and content management systems all can benefit from a standard, human- and machine-readable way to describe and identify content.
Skipping a few numbers, we get to the last of the brewing standards – the MPEG-21 Multimedia Framework. MPEG21 seeks to let content distributors have complete control over content at all parts of the delivery chain and on all kinds of networks and devices. The basic idea is that digital media content is broken down into digital items. An item might be a video data stream, an audio data stream, subtitle text or the URL to a logo image, all within one MPEG21 file.
Using the “adaptation” feature of MPEG21, networks or playback devices can interact with specific items in the file. For example, you might have multiple audio tracks in different languages all packed in one file. The playback device would understand the options and rules, and play the appropriate one for the user. With the delivery system having knowledge of what’s inside the file, the intent is to allow seamless access to media across all kinds of devices and networks, regardless of bandwidth or client capability.
Perhaps the MPEG21 feature that has received the most attention is its DRM (Digital Rights/Restrictions Management) system. To maintain control over the dissemination and use of digital content, MPEG21 aims to assert total control over usage. Every digital item has granular rights and permissions associated with it, and every user who interacts with it – consumers or content providers – are granted specific rights according to their role.
Total control over the file’s behavior for any purpose on any device or network, along with extensive restrictions and role-based authorization, will result in two possibilities. One is an ubiquitous and standardized capacity to do eCommerce with digital media in any environment – be it server-based, peer-to-peer, or “sneaker net.” The other is that, without proper legal and technical safeguards, you also may be granting too much power to the content owner to control the way the media is consumed.
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