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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
JARGON FILTER
PAL/NTSC
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.
RIPPING
Extracting
encoded data from audio CDs and DVDs, so it can be re-recorded or converted to
another other format
SVGA/VGA
Super Video
Graphics Array - display formats used on PCs, defined by the number of picture
elements (pixels) and colours used to create an image
TOP TIP
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.
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© R. Maybury 2006, 3001
Part 1 2 4
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