Video file formats are a complicated field
filled with endless acronyms, jargon and confusing file extensions. As an HTPC
user it is unfortunately essential that you try to understand some of this
jargon, because you will experience much of it when downloading content and
using the most popular video encoding and decoding software.
Uncompressed video files are absolutely vast
and can occupy tens or even hundreds of gigabytes of space on a hard drive per
file. For all but the most specialised applications we therefore have to apply
various compression algorithms that reduce the amount of space these video
files take up. The method of compression used has a great impact on the quality
of the end result, with some methods resulting in a huge reduction in both
picture quality and file size while other more modern methods minimise the
noticeable quality degradation, but can still greatly reduce the storage space
required.
AVI
AVI is one of the oldest formats of any
kind still in use, being created by Microsoft some 14 years ago. Contrary to
popular belief, an AVI is not a type of video format, but is actually a wrapper
or container file. It holds the video and audio information data, but the data
is read from the AVI file by codecs. There are a great many codecs available,
with popular examples including DivX, Xvid, and MJPEG. There is therefore no
way of knowing if an AVI file you have created will be compatible with a given
player without full knowledge of what codec packs have also been used during
its creation.
Codec is an acronym for "Compressor /
DECompressor" and relates to any technology for compressing and
decompressing data. They can be implemented in software, hardware or in a
combination of both. All media players use codecs, with various pros and cons.
Examples of popular codecs are MPEG, DivX, Xvid and H.264/AVC.
MPG
The MPG (often also seen as .mpeg) format
is derived from an acronym of the Moving Picture Experts Group; an organisation
tasked with the development of advanced audio and video encoding standards.
Mpeg, pronounced 'em-peg', can encompass a number of different file formats,
though files of this type are usually either MPEG-1 or MPEG-2 files.
MPEG-1 video file formats are ideal as a
vessel of choice for the distribution of small, basic videos. Because of the
format's age it is supported natively by just about every capable video player,
including all recent versions of the media players bundled with Windows
operating systems. If, for instance, you've created a short video clip of
something amusing that happened to you while on holiday, MPEG-1 would be an
ideal video file type to use when distributing it to your long-suffering
friends and family, because in all likelihood they could all view your capers
without the need to install any further software.
In 1994 the MPEG group ratified the MPEG-2
format. It was designed from the ground up to produce higher quality images at
higher bit rates than MPEG-1 for situations where greater bandwidth was
available. It is in extremely wide use as the video file type used in DVD
video. The optimum bit rates for MPEG-2 are from 3-10 MB/s. MPEG-2 is usually
displayed at a resolution of 720x576 (PAL) or 720 x 486 (NTSC), and at these
resolutions it provides broadcast quality video. MPEG-2 was specifically
designed so that any decoder designed for it would also be backwards-compatible
with MPEG-1 streams as well -this is why most DVD players can also read VCDs.
As well as in DVDs, MPEG-2 video can also be found in SVCDs, as well as in
standard definition digital TV broadcasts.
Work on MPEG-4 started in 1995 and was
primarily designed to give large improvements in image quality for lower bit
rates. MPEG-4 is ideally catered for files on the internet and variations on
the codec such as DivX and Xvid allow an AVI with high video quality to be
presented on a file as much as 10 times smaller than an MPEG 2 equivalent.
MPEG-4 files do not use the .mpg format and are typically found as either AVI
files (when they have been created with DivX, Xvid and others), MOV when
created using QuickTime's MPEG-4 encoder, MP4, which is the official MPEG-4
file extension (and an advanced container format similar to avi), or MKV.
