The next logical step in
delivering graphics over the Web is to deliver animiated
graphics and/or video. The main challenge with video is the
file size and bandwidth requirements which can potenially
equate to hundreds of megabytes as well as lengthy delivery
times. Video poses an even greater problem than graphics with
regards to bandwidth and performance. Once again a motivation
is created to reduce or compress the size of the file while
not denegrating the quality of the picture. The topic of
video optimization is extremely broad and complex, but the
following will provide a thirty-thousand foot high view.
The most common formats used
for delivery over the Web are the following: AVI, MOV, MPG. A
new form of video delivery, ASF or Advanced Streaming Format,
is also becoming popular over the Web. ASF is currently a
much better method than any of its predacessors.
AVI ... AVI
stands for Audio Video Interleave and was developed by
Microsoft. It is the most common video format for the PC,
but it does not offer the compression advantage the MPEG
has. AVI is equivalent to the bitmap for graphics. It is
the video file format without optimization and is the
starting point for further compression methods.
MOV ... MOV is
the PC file extension used for QuickTime
"movies". QuickTime is an Apple product which
is very popular with games. This is old technology and is
not a preferred method for Web delivery, but it is still
used sometimes.
MPEG ... MPEG
stands for Moving Picture Experts Group (a working group
of ISO) and uses a file extension of MPG. MPG is
pronounced M-PEG. MPG is a family of standard compression
formats which were developed by the Picture Expers Group.
It is popular because of the reduced size of the
compressed video as well as the fact that the quality is
better than some of the other choices. To view the MPG
format a user must have the proper hardware and software.
Like its graphic counterpart, JPEG, MPEG uses lossy
compression to optimize moving images. There are two
types of MPEG files, MPEG-1 and -2. MPEG-1 offers
resolution of 352-by-240 at 30 fps (frames per second).
MPEG-2 is newer and offers resolutions of 720x480 and
1280x720 at 60 fps, with full CD-quality audio. MPEG-2 is
what is used with the new DVD technology and is capable
of compressing a 2 hour movie into a few gigabytes. The
next generation of MPEG will be MPEG-4 and will be based
on the QuickTime file format.
ASF ... ASF is
exciting technology for anyone involved with the Web. ASF
stands for Advanced Streaming Format and was developed by
Microsoft. A new tool suite called NetShow is available
from Microsoft to convert AVI files to ASF files, but ASF
offers a higher compression rate than AVI files. ASF is a
set of rules for describing how multimedia data is
organized and laid out on disk. These rules are optimized
for streaming the data over a network, and for playing
back the data at the client end. The data stored in the
ASF format can represent dynamic, advanced multimedia
presentations. What makes ASF files so unique and so
preferable is that while other methods require that the
entire file be transferred to a user's PC, ASF sends
enough to get you started, so you don't have to wait for
everything. This is accomplished because ASF files are
made up of a collection of data objects which share basic
characteristics. These shared characteristics are three
fields: (1) a 16-byte-long field containing a GUID; (2)
an 8-byte-long field containing the size of the object;
and (3) a field as long as the second field (minus 24
bytes) containing data of some kind or other. GUIDs are
unique identifiers of objects.
Together with AVI, older
multimedia technologies such as MPEG-1, MPEG-2, and QuickTime
have set the stage for the digital multimedia revolution.
Through them, digital multimedia has become a reality.
However, like AVI, these older technologies were not
originally developed with Internet delivery and Web
presentation in mind; hence, it is natural that MPEG-1,
MPEG-2, and QuickTime are less than optimal than ASF for
streaming synchronized multimedia presentations in the new
internet environment.
Hyperlinks for Further
Research:
MPEG Pointers and Resources:
http://www.mpeg.org/MPEG/
Resource for
information on MPEG covering FAQs, industry news, audio and
video players, systems, companies, products, and shareware
Video
on theWorld Wide Web:
http://www.videonics.com/videos/about-web-video.html
Discusses on-the-fly
video delivery and the necessary compromises. Includes links
to more information about MPEG and the advantages and
disadvantes of streaming video.
About
ASF:
http://www.microsoft.com/asf/aboutASF.htm.
Contains an overview
of ASF and answers to common questions.
The Audio & Video Compression Page:
http://www.fedele.com/website/compress/compress.htm.
Good collection of
links to technical MPEG and JPEG FAQs, as well as audio and
video compression information and an introduction to wavelets
AVI
Overview:
http://www.rahul.net/jfm/avi.html
Excellent overview of
Video for Windows, ActiveMovie, and AVI written by John F.
McGowan. Includes information on utilities, system
administration and authoring, as well as installation,
configuration, programming information, and technical topics.
