MPEG-4 ASP

MPEG-4 ASP, or Active Simple Profile, is a video Compression standard defined in MPEG-4 Part 2. The most common implementations of MPEG-4 ASP are probably DivX and XviD, although a number of other codecs are also available. Being a standard, rather than a specific Codec, any decoder certified to playback MPEG-4 ASP can play standards compliant video encoded with any tool. In other words, a DivX decoder should have no problems playing XviD video.

MPEG-4 ASP History

Being originally designed primarily around commercial Streaming uses like video conferencing, MPEG-4 didn't get a lot of attention from the public until the leak of some Microsoft code for a new WMV (Windows Media Video) compression format based primarily on MPEG-4 Part 2, which includes ASP among its 21 profiles. The code was distributed as DivX ;-) 3.11 Alpha.

Project Mayo

The availability of the Microsoft source code generated enough developer interest to start Project Mayo, also called OpenDivX. Development of OpenDivX would end when the original developers decided to create a commercial encoder, and formed DivXNetworks. Their DivX codec was largely responsible for early consumer interest in MPEG-4. Other developers decided to continue open source development, and went on to create XviD. As both codecs matured more companies took notice and a number of MPEG-4 ASP encoders are being sold.

Container

As there was no official MPEG-4 Container until after the development of MPEG-4 AVC (H.264), early MPEG-4 hobbyists found that Microsoft's AVI container could be used to hold MPEG-4 video and MP3 audio. However, with the advances in both containers and consumer software there are far better containers, such as MP4 (the official MPEG-4 container), MKV (the Matroska container), or even MPG (MPEG-2 Program Stream) are better alternatives, both for support of modern video encoding features and portability from one operating system to another. AVI is a Microsoft and Windows specific format.

Hardware Support

With the release of the KISS DP-450 in 2002, MPEG-4 ASP Decoding was available in a standalone DVD player for the first time. AVI files had to be used, and there were issues with a number of MPEG-4 ASP features. Despite the issues a market that's grown to include official certification programs from multiple codec vendors, including DivX, XviD, and Nero Digital, exist. In addition to AVI support, many newer players also support the MP4 container. DivX has even created an extension to the AVI container to allow the use of simple menus, similar to a very basic DVD.

MPEG-4 Part ASP Features

MPEG-4 ASP shares some features with MPEG-2 video encoding, but also differs in some significant ways. Being part of the MPEG-4 family it's somewhat more efficient, although not as efficient as MPEG-4 AVC, which was developed later. This means smaller file sizes than an MPEG-2 file with comparable quality.

Interlaced Video
Although supported by the ASP Profile, interlaced encoding isn't available in all encoders. Since MPEG-4 support in DVD players was non-existent in the early days of MPEG-4 encoding, and HTPCs were also rare, almost everything encoded for the first few years of DivX development was Progressive to match computer monitors they were being viewed on. As the majority of sources come from film, and are therefore also progressive, this wasn't really a problem. However, if you're encoding for display on an analog TV, such as through a standalone DVD player, you'll probably want to make sure you're using a codec capable of interlaced encoding. Fortunately this has become a fairly standard feature for encoders and decoders.

B Frames
The other commonly implemented MPEG-4 Profile, Simple Profile or SP, is intended for use with low powered CPUs. As a result no B Frames are allowed. B frames, or Bidirectional-Predictive Encoded frames require two reference frames to be decoded, compared to the single reference Frame required for P frames. Since ASP isn't designed with this hardware limitation in mind it supports B frames.

Qpel
Quarter-Pixel Motion Compensation allows the calculations used to detect motion (for prediction purposes) to be more accurate than MPEG-2. Although obviously you can't store less than a whole pixel, that doesn't mean movement in your video will be in 1 pixel increments. By increasing the precision to 1/4 of a pixel (from MPEG-2's Half Pixel precision) prediction is improved, sometimes meaning better quality at a comparable Bitrate. Older standalone DVD players with MPEG-4 ASP support won't playback files encoded with Qpel, but it shouldn't be a problem for newer models.

The Future

With the finalization of MPEG-4 Part 10 (AVC/H.264), and its subsequent adoption for use in technology ranging from mobile phones to digital TV and Blu-ray movies, it has already effectively made MPEG-4 ASP obsolete. As AVC decoders aren't capable of decoding ASP video this means more, or at least more complex, hardware for standalone DVD players to support both. With AVC's superior compression and image quality there's little reason to stick with MPEG-4 ASP too far into the future.

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In the News 27 March 2000 - Big boys are getting worried about DivX ;-) Major news agencies on the web are raported about this pretty-familiar-to-aD-users technology called "DivX ;-)" that is based on MPEG4 video and MP3 audio compression.... (Read More) 19 July 2001 - DivX Codec v4.0 beta released Project Mayo/OpenDivX/DivX.com (man, these guys have more projects than us ;-) released a new version of the DivX Codec, version 4.0 beta.... (Read More) 23 August 2002 - XviD source code abused by Sigma Designs XVID is a leading open source MPEG-4 video research project, founded by the German student Michael Militzer in August 2001 to continue the efforts of DivXNetworks' former OpenDivX project.... (Read More) 22 October 2002 - First DivX compatible DVD player launched KiSS Technology was one of the first MP3/DVD hybrid player providers few years ago, based on the same technology as Raite, Yamakawa and few other clones. Now they are the first brand announcing DivX support.... (Read More) 27 November 2002 - MPEG-4 licensing details released After months of negotiations, public outcries and protests from media companies, MPEG LA finally released its licensing contract for MPEG-4 video (including Simple Profile and Advanced Simple Profile).... (Read More) 1 March 2004 - XviD v1.0 RC 3 released Koepi's binary version of XviD codec has been updated to XviD v1.0 RC 3 and the final 1.0 release should be just around the corner.... (Read More)