BOOT CAMP 463 (13/02/07)

Multimedia Formats and Codecs part 4


This week we conclude our brief guide to computer multimedia with the final group of digital video formats and we begin with one that might sound familiar. It’s M-JPEG, or Motion JPEG, and the JPEG part is essentially the same lossy data compression system most digital cameras use (see part 2) to record still images. The M-JPEG format is not as efficient at capturing movement as some of the other formats we’ll be looking at and file sizes can be quite large but it does have a number of important applications where still image quality is important, such as time-lapse or surveillance video recording. An enhanced version of the format called M-JPEG 2000 has been specifically developed for this purpose. M-JPEG is also widely used by web and network or ‘IP’ cameras and some digital still cameras use it for recording ‘movie’ clips.


The largest group of digital video formats is a set of standards defined and managed by the Moving Picture Experts Group or MPEG, a division of the International Standards Organisation (ISO). MPEG-1 was the first to appear in 1991 and was used by Philips and Sony for the short-lived Video CD or VCD format. It had limited success in Europe, VHS remained the technology of choice for home video recording and movies, but it did take off in many Asia-Pacific countries where it was used in karaoke systems and because of its simplicity and the low cost of hardware it proved very popular with movie pirates.


Compression levels are quite high so file sizes are relatively small – a 90-minute movie fits comfortably onto a 650Mb CD – but picture quality is fairly average and not much better than VHS tape. MPEG-1 is now virtually obsolete but its audio compression system, known as Audio Layer 3, lives on and is better known as MP3.


The best-known member of the MPEG family is MPEG-2, which was introduced in 1994 and is now used by most of today’s digital video and TV technologies, including DVD, terrestrial and satellite television and High Definition television (HDTV). MPEG-2 employs a number of methods to reduce the amount of data in a video file, including stripping out colour information, such as fine graduations that the eye cannot perceive. However, the most effective technique is temporal redundancy. This is an ingenious trick that works on the basis that successive frames of video or a movie are normally very similar to each another -- the sky or background are the same, for example -- so rather than encoding every tiny detail in every frame, only the parts that change need to be processed. Most of the time it works very well, but at higher compression levels processing effects can be quite noticeable. Images with a lot of rapid movement can overwhelm the decoder and appear ‘blocky’ (motion artefacts) and textured backgrounds may appear strangely static.


MPEG-2, in common with most digital video systems is a ‘container format’  (see part 3), it is highly versatile and in addition to video and multi-channel and multi-lingual sound it can also contain other data streams, such as interactive programme guides and Teletext.  


In the mid 1990s the MPEG-3 made a very brief appearance; it was intended for HDTV applications but it was dropped in favour of the constantly advancing MPEG-2 format.


MPEG-4, on the other hand was an almost instant success and it pops up all over the place. The standard was ratified in 1995 and was initially conceived as a highly compressed, low bitrate system for undemanding applications, such as videophones, but it rapidly evolved into several sub-formats and derivatives, such as DivX (see part 3). In some cases picture and sound quality is approaching that of DVD/MPEG-2, but with substantially smaller data files and lower bitrates. MPEG-4 is proving particularly popular on portable devices, including camcorders and personal media players, where storage space, processing power and battery capacity are at a premium.


QuickTime (extension .mov) is the granddaddy of multimedia container formats and still widely used on the Internet. It was developed by Apple in 1991 but since then it has undergone many revisions and now encompasses a wide range of codecs and compression schemes, including ones specifically designed for animation, graphics and streaming over the Internet. Recent versions of the QuickTime player (for both Mac operating Systems and Windows) now support MPEG1, 2 and 4 plus a wide range of lesser-known codecs.


RealVideo from RealNetworks is a streaming format for sending low and medium quality video over the Internet that can be viewed live with RealPlayer software. Version 1 was launched in 1997 and since then a number of changes have been made but throughout RealNetworks has used proprietary codecs. This places restrictions on the software use to create videos, and multimedia players able to decode and process the data stream. With rival formats now delivering similar and in some cases superior performance it is becoming less popular.


WMV or Windows Media Video (extension .wmv) is the most recent of the mainstream digital video formats and the first version of the codec, based on Microsoft’s own version of MPEG-4, was announced as recently as 2003. Benefits include high compression levels without serious loss of quality, making it ideal for Internet applications where it is used for both streaming live video and file downloads. WMV files and streams can be replayed on Windows Media Player and it is supported by a number of other popular media players.


Next Week – VCR and Camcorder to PC and DVD





A measure of the amount of digital data a system can process, measured in bits per second or 'bps',



A video camera or webcam with a built-in web-server, enabling it to operate independently of a PC, streaming live video over a network or the web from it’s own unique IP (Internet Protocol) address



Technique used to send sound and pictures over the Internet. Data is 'buffered' or stored in a temporary memory by player software on the PC to minimise the interruptions that would otherwise occur as data on the net is sent in chunks or 'packets'.




Last week we suggested Media Player Classic as a lean and simple to use alternative to Windows Media Player, but if you are looking for something a little more sophisticated, yet still without the unnecessary features and intrusive nature of WMP then take a close look at Mplayer. It’s an Open Source program and it is in a constant state of development. Installing it in its ‘raw’ state can be quite a challenge for novices but there are a number of compiled packages available that combine all of the components in one download 


 © R. Maybury 2006, 0702

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