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"But like anything in the realm of computer technology,
the video we watch is wrapped up in a morass of jargon and of weird
extensions."Video may have killed the radio
star, but it's become more than just something that we watch on our
televisions. Video is definitely an essential part of the
desktop and Web experiences of most computer users. And more
than just a few mobile phone users, to boot.
But like anything in the realm of computer technology, the video we
watch is wrapped up in a morass of jargon and of weird extensions.
If you don't know your .avi from your .mov or .flv, then read on.
Formats vs. container formats
When it comes to other kinds of files, we all have a pretty good
idea of what a file format is. We know that a Word file is
a binary that contains all of the text that we've typed into the
word processor, the style information, and graphics too. But the
situation is different with video.
When people talk about video formats, they're referring to something
called a container format. The container format is a
detailed description of what's inside a video file. It describes the
structure of the file, as well as the kind of data that the file
contains.
The container format also holds information about something called a
codec. The codec is information about how the file was encoded,
specifically what software (called a codec, not surprisingly) was
used to digitally encode the file. This is important, especially for
a couple of the formats that are described in this TechTip. Why? Not
every media player supports the same codecs. In many cases, you'll
need to install a specific codec in order to play a file using your
favorite media player.
MPEG
 MPEG
is short for Motion Picture Experts Group. It's a standard for both
a variety of video and audio formats, and for compressing those
formats. In fact, the array of formats that use MPEG compression can
be confusing.
There are different versions of the MPEG format (often called
levels) which help contribute to this confusion. The three MPEG
levels that you're likely to encounter are MPEG-1, MPEG-2, and
MPEG-4.
What's the difference between all of them? MPEG-1 is the oldest of
these. It was first used in video CDs (the precursor to the DVD),
where space was at a premium. MPEG-2 tackled (and still does) the
transmission of digital and high definition over digital networks,
satellite TV, and (later) the Internet. In fact, MPEG-2 is so
efficient that it pretty much killed off MPEG-3 -- it handles high
definition video just as well as its descendant. MPEG-4 does pretty
much everything MPEG-2 does, but with better quality and
compression. MPEG-4 adds another twist to the mix: it supports
Digital Rights Management (DRM), which enables content producers
to prevent copying of their content.
Note: An upcoming TechTip will look at DRM and its
implications.
If you run into any video files with the extension .mpg or .mp4 you
have an MPEG file on your hands. It's a popular format because it
provides a good tradeoff between file size and quality. Just about
every media player supports MPEG, although some players support the
format better than others. I've found that it's a rare MPEG file
that won't play on the various media players that I use in Linux or
on Windows.
AVI
If there's a format that doesn't get a whole lot of respect it's AVI
(short for Audio Video Interleave). Originally developed for
Microsoft Windows, AVI has become ubiquitous across several
operating system and on the Web. While it isn't as popular as it
once was, it's not rare for you to run into AVI files
AVI files, which have the extension .avi, are often disparaged from
a couple of reasons. First, they use little or no compression. That
means the file sizes are larger than just about any other format out
there. And AVI files often use a variety of codecs to encode them.
This causes trouble, because you might not have the proper codec
installed for your media player and the file won't play. This is
especially true on operating systems other than Windows. It's not
uncommon for an AVI to not play on Windows without the proper codec.
Windows Media Player can sometimes automatically download that
codec, but usually you'll have to search for it yourself.
Since it's an established format with a long history, you'll find
that most media players for Windows, Mac OS, and Linux can handle a
number of AVI files. The one player that I've found which works best
is
VLC.
WMV and ASF
 Windows
Media Video (WMF) and Advanced System Format File (ASF) were created
in part to deal with the shortcomings of AVI.
WMV is a compressed file format (at least, with better compression
than AVI) with the extension .wmv. It was developed primarily for
streaming video across the Web. Microsoft claims that WMV has better
file quality than MPEG. That may or may not be true, but WMV files
are generally larger than MPEG files. Often by a factor of two.
ASF, on the other hand, is a container format for WMV. It
encapsulates not only the video and audio data for a WMV file but
also Windows Media DRM data. All of this is wrapped in a file with
the extension .asf.
The biggest criticisms of WMV and ASF are that they're specific to
Windows, and that ASF supports very restrictive DRM. As for the
first complaint, it is possible to play WMV files on other operating
systems. On Mac OS, for example, you can get a player called
Flip4Mac WMV which enables you to edit WMV files and convert
them to QuickTime. This allows you to play WMV files on not only
your Mac but also on your
iPod. On Linux, the VLC and
xine players can handle WMV files that don't have DRM applied to
them. Well, at least most of the time.
And that's the main point of contention with the second complaint.
DRM-protected WMV and ASF files generally won't play on other
operating systems, or with anything other than Windows Media Player
on Windows. An interesting aside is that Microsoft's
Zune player doesn't support Microsoft's DRM scheme so you can't
play WMVs with DRM applied to them. Ironic, isn't it?
Flash Video
 Once
upon a time, Flash was used almost exclusively to create demos,
tutorials, and annoying splash pages for Web sites. Now, thanks to
the popularity of video sharing sites like
YouTube, Flash has become an almost ubiquitous video format.
Most Flash video files have the extension .flv or .swf, although you
might see the files with the extension .f4p (protected Flash video).
Flash is usually used for streaming video across the Internet, and
is able to do this quite efficiently because files can be compressed
to make them smaller.
 The
compression can be a bit of a problem, though. The main codec used
to encode Flash files is based on
bitmap images -- each element and frame in the video is a set of
pixels. When pixels are compressed, they become fuzzy and lose
varying amounts of color depth. You've probably seen badly
compressed Flash videos on YouTube. They're blurry and look washed
out.
Flash is more or less a cross-platform format.
Adobe Systems, which owns and develops the software that enables
people to create and view Flash video, has Flash players for
Windows, Mac OS, and Linux. On top of that, a number of media
players (such as
RealPlayer, Windows Media Player, VLC, xine,
Gnash, and QuickTime Player) support Flash. Some of these
players only support older versions of the Flash format, though.
QuickTime
 Whereas
Windows has AVI (and now WMV and ASF), Mac OS has QuickTime. You can
tell that you have a QuickTime file if you see the extension .mov or
.qt.
QuickTime is a compressed format, using a compression scheme
developed (and closely guarded) by Apple. This compression scheme is
very efficient, and can noticeably shrink the size of a file but
without losing much of the quality. In fact, QuickTime files
arguably offer some of the best quality video available.
 One
interesting characteristic of the QuickTime format is that it
contains multiple tracks. Each track contains different types of
data. For example, one track will contain audio, the second video,
and the third subtitles. This separation of content makes a
QuickTime file easy to edit.
QuickTime files are usually best played using Apple's own
QuickTime Player, which is only available for Mac OS and
Windows. You can also
download add-ons for Windows Media Player to enable it to play
back QuickTime files. On Linux, the
MPlayer and xine media players can handle QuickTime although you
might need to install additional codecs.
3GPP Multimedia
People don't just watch videos on their
televisions and computers anymore. More and more, they're
watching them on their smartphones as well. Whether it's an iPhone,
a BlackBerry, or one of the many phones from companies like Nokia
you can get and watch high-quality video on a device that literally
fits in the palm of your hand.
One format that makes it possible is 3GPP multimedia. 3GPP (which
has the extension .3gp) is one of those container formats that I
mentioned at the beginning of this TechTip. It was created to move
audio and video to mobile phones -- either from phone to phone via
email or MMS, or over the Internet.
Most modern smartphones, especially ones with built-in video capture
and playback, will play and record 3GPP files. Like other formats,
the quality of 3GPP files varies depending on the resolution of the
camera used to capture the video and the compression options that
were used when saving the file. Obviously, the higher the
compression rate, the lower the quality of the video. I've received
video taken with a smartphone that was fuzzy, and video that's been
as clear as the best MPEG files I've seen.
While just about any smartphone will play 3GPP files, on the desktop
only a handful of media players can handle these files. The
best-known ones include VLC, RealPlayer, MPlayer, and Apple
QuickTime Player.
Conclusion
This TechTip only describes the video formats that you will
routinely run into. There are literally dozens more out there. You
can find some basic information about various formats
here, or by visiting
Wikipedia. |
