An MPEG Primer

As a media professional that must deal with all types of people with many different requests on any given day, I've learned one thing....don't assume that what people tell you that they want is actually what they are asking for.

Let me explain. With computer files being exchanged between people on a very frequent basis, people often don't communicate what they need correctly. When I make media files for clients that are to be delivered on a computer storage medium, the clients often assume that I know what kind of files, and what specifications they desire. I often hear things like,

"Well just make a graphic file that I can open up on the computer at my office."

--or--

"You know, the kind of file that I need to go on my website."

Upon hearing these type of things, I probe further asking for file formats, sizes, resolutions, and any other information that applies. I find that many people don't know this information. That is okay because I understand that many people don't deal with the intricacies of computer file specifications often enough to know this information off of the top of their heads. A brief interrogation about use and intended audience usually gives me a good enough idea of what speicifications I should use.

One of the more misunderstood group of file formats is MPEG. There have been thousands of informational treatises written about this, and many technical papers. I just plan to offer a brief primer.

The main reason for MPEG files being developed was to allow media developers to spend their time worrying about the content rather than the medium.

I) MPEG-1 was developed by the Moving Picture Experts Group to facilitate the digital storage and transfer of audio/video information. This would allow a reasonable amount of video to be stored on a computer hard drive and would also allow transfer of motion picture "rough cut" information across high speed phone lines. I won't go into a big description of the encoding/decoding process. Basically the computer broke a picture into blocks at regular intervals, and based upon the changes between these blocks taken from different points in time, interpolated what should go in between them to make the proper motion between them.

MPEG-1 accomplished three very important things. It allowed data rate speeds of 1.2 to 1.8 Mbps (T1 line or single-speed CD-ROM). It allowed video to be stored with the quality of a VHS tape. Most importantly, it allowed metadata streams. (Metadata is data that is not part of the audio or video, but data that contains information about the file. Metadata sent with the audio/video stream is analogous to having the ability to tape an envelope full of instructions to the film canister being shipped).

II) MPEG-2 was developed with the purpose of improving quality over the MPEG-1 format. (Pretty common sense, huh?) The specifications were made in a forward thinking manner with the knowledge that DTV applications would show the limits of MPEG-1. The new specification allowed data rates up to 100 Mbps (faster data rates mean better quality). The new MPEG-2 standard also permitted scalability.

III) MPEG-3 was developed with HDTV applications in mind. The specification standard was never finalized and was aborted because the MPEG-2 standard was found to be sufficient to accomplish the needs of HDTV applications. (NOTE: MPEG-3 is NOT, I repeat NOT, the same as mp3. MPEG-3 IS NOT mp3! mp3 files are actually MPEG-1 Layer 3 Audio for stereo audio (ISO/IEC 11172-3) or MPEG-2 Layer 3 Audio for 5.1 surround audio (ISO/IEC 13818-3))

IV) MPEG-4 was developed with multimedia content providers (outside of the broadcast/movie arena) needs a little more the focus. MPEG-4 gave all the benefits of MPEG-2, but took a more object-oriented approach. This standard can provide all the interactivity found in things like computer games and DVD-Video interactive menus because in treats media as "objects" rather than audio/video program material.

V) MPEG-7 is currently being developed (yeah, I know, they skipped 5 & 6). The main focus of this standard is to offer a globalized standard for APIs (Active Program Interfaces) so that media can be handled more flexibly and easier across any MPEG-7 compatible device. It should help the convergence taking place between the computer and entertainment industries.

I strongly encourage anyone interested in the technology of MPEG standards to do some investigation. The process that occurs to actually compress that audio/video data is actually quite interesting both mathematically and conceptually. Unfortunately, it is too large a subject for me to cover in a web article.

©2001 Eric Kilgore used with permission. This article first appeared on www.theoreticalreality.com website. Eric Kilgore spent ten years as a professional audio video engineer and producer before entering the computer field full-time