BOOT CAMP 462 (06/02/07)

Multimedia Formats and Codecs part 3


Watching movies on a computer is taken pretty much for granted these days but it is a comparatively recent innovation and as recently as five years ago you would have struggled to find a home PC capable of displaying high quality video, let alone one able to edit recordings and burn DVDs.


The frenetic pace of development has cause a lot of problems, though, resulting in a bewildering array of file formats and compression technologies. And it’s not going to get better anytime soon with new gadgets and the web generating ever more ways to create, view and distribute live and recorded video.  


At the last count there were more than 50 digital video systems and that’s not counting computer display formats (VGA, SVGA etc.), or the various analogue formats and standards (PAL, NTSC), which become relevant if you ever want to use your PC to compile DVDs from old VCR or camcorder tapes – more about that in a forthcoming Boot Camp.


Fortunately you really only need to know about a few of them – ten at the most – but that is more than enough to get you into a tangle should you ever want to edit or convert video files, However, before we begin it is important to deal with the slightly tricky concept of ‘Container Formats’.


Unlike a text file, digital image or even an audio track a video recording is not a single entity. Most recordings also have a soundtrack or ‘audio stream’ – sometimes several – as well as various other data streams. It helps to think of a video file as a receptacle or container for several different types of audio and video data and its extension is a way for the computer to identify the program that can open and unravel what’s inside, using the appropriate decoder programs or ‘codecs’. So let’s start with the first batch, more next week.


AVI or Audio Video Interleave (extension .avi) is one of the oldest surviving multimedia Container formats and because it was developed by Microsoft, as a component of its Video For Windows (VFW) technology it has become an industry standard. VFW was a response to Apple Computer’s early lead in multimedia with the QuickTime format (see part 4); it was introduced in 1992 and has been fully integrated with Windows from Win 95 onwards. Clicking on an .avi file normally opens Windows Media Player, though it is recognised by many other popular media players, which have the appropriate codecs. The quality of an .avi file varies as the data can be compressed using a variety of different methods.


Our next format is AMV, which probably stands for Apex Media Video (extension .amv). The reason for the confusion is that it is very new and has a slightly shady background. It is almost certainly Chinese in origin and possibly derived from a Nintendo format developed for the Gameboy console. The AMV format first appeared about a year ago, on the back of an influx of cheap MP3 players with tiny video screens, (also known as ‘S1 MP3’ players). AMV software, supplied with the players converts or ‘rips’ DVDs so they can be viewed on the player’s screens. It works by reducing the size of the original image (typically to just 196 x 96 pixels), discarding any fine detail and halving the frame rate. In this way a 2-hour move can be packed into 100Mb or less space. The decoding process requires very little computational power and is therefore less demanding on the player’s limited battery resources. It’s an impressive feat but it has to be said picture quality is dire and you need to be fairly determined to watch a fuzzy, jerky movie on a 1.5-inch LCD screen...


We’ll finish off this week with DivX (extension .divx), a fast developing and increasingly popular set of codecs, also with a controversial history. DivX is a brand rather than an acronym and it owes its origins to a French hacker called Jerome Rota, who in 1998 managed to reverse-engineer a Microsoft multimedia codec (MPEG-4, see part 4 next week). Rota made his work public and in 2000 DivX.Networks (now DivX inc.) was formed to oversee its development. Over the following years a number of improvements were made, culminating in version 5 of the codec in 2002, which is the basis of the format in use today and now widely used for ‘ripping’ DVDs and encoding video recordings for viewing and distribution on the Internet and replay on a wide range of devices.


The key benefit of DivX is highly efficient compression, which reduces file sizes but without sacrificing picture and sound quality to the same extent as some rival compression schemes. From its slightly dubious beginnings DivX has now become a respectable mainstream format, supported by a growing list of products and devices, including digital still cameras, like the Pentax Optio A20, which takes DivX encoded movie clips, portable DVD and media players such as the Toshiba SD-P2800 and Lyra X3030 and Roxio’s Easy Media Creator 9 CD/DVD authoring suite. Software for replaying and creating DivX videos is also freely available on the Internet. 



Next Week – Multimedia Formats and Codecs part 4





Phase Alternate Line/ National Television Standard Committee – colour television technical standards, PAL is used throughout most of Europe, the Middle East, Africa and Australia whilst NTSC is mostly used in the US and Japan.



Extracting encoded data from audio CDs and DVDs, so it can be re-recorded or converted to another other format



Super Video Graphics Array - display formats used on PCs, defined by the number of picture elements (pixels) and colours used to create an image



Most PC users tend to stick with Windows Media Player (WMP), which comes with Windows, and very good it is too, but over the years it has fat and bloated, packed with features and functions that may be seldom used. There are plenty of alternative media players but one of the best is a small freeware program, based on an earlier version of WMP, called Media Player Classic. It’s versatile and plays everything from MP3s to DVDs, it’s fast to load and very easy to use.



 © R. Maybury 2006, 3001

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