A   S t r e a m i n g   M e d i a   P r i m e r :  
H O W   D O   I   M A K E   ( G O O D )   S T R E A M I N G   M E D I A ?
But even reducing both the frame size and the frame rate does not reduce the bit rate 
of video fi les enough for effi cient streaming. So additional methods for compressing the 
  bloated streaming media 
amount of data that needs to be transmitted are used. We haven't space here to go into 
has a tendency to alienate your 
too detailed a discussion, but the following general descriptions will give you a general 
site visitors. Your clip may look 
understanding of compression methods.
good off your LAN on your fast 
Intra frame compression:  Derived from still formats, intra frame compression, also 
known as spatial compression, treats each frame individually. Some spatial compression 
CPU. But if it looks like junk 
schemes work by discarding much of the color information in the picture. As long as this 
to your user, you have just told 
type of compression is not too severe, it is generally unnoticeable. In fact, in even the 
highest quality  uncompressed  video used by broadcasters, some of the original color 
them that you do not need 
information has been discarded. Avoiding  hot  colors and harsh contrast when shoot 
their business... Do the band 
ing helps ensure the best results from this type for compression. Spatial compression 
works best on continuous tone images without sharp edges, such as photography and 
width math. Test on a slower 
videography (as opposed to animated graphics). The softer and smoother the imagery, 
CPU. Take as many people along  
the better results you'll achieve with systems that use spatial compression.
for the ride as you possibly can. 
Inter frame compression:  Inter frame compression, also known as temporal compres 
sion, takes advantage of the fact that any given frame of video is probably very similar to 
 Tim Kennedy
the frames around it. So, instead of storing all the information for each and every frame, 
Streaming Media World
47
temporal compression schemes store keyframes in their entirety, while delta frames 
(comprising the majority of frames in Web video) contain only the information that 
is different from the keyframes that come before and/or after. You can usually specify 
A codec (set of mathematical 
how frequently keyframes occur less frequent (and, therefore fewer) keyframes mean 
smaller fi les, but will also result in lower quality, since more frames will need to be 
algorithms) is used by an encoder 
inferred, or  predicted,  from keyframe information.
(component of an architecture that 
What is a codec?
produces fi nal streaming fi les) to 
Compression and decompression are accomplished by a set of mathematical algorithms 
compress (reduce the data rate of) 
called a codec short for  compressor/decompressor.  Codecs compress data as it is 
digital video and/or audio. The player 
encoded, and decompress it for playback. In order to be played, a fi le compressed with a 
certain codec must be decompressed by the same codec. 
(client component of an architecture 
While the codec itself is comprised of software code, a codec may be a part of either a 
that plays back media fi les) must use 
hardware or a software solution. For example, an  onboard  codec may be found in a 
the same codec to decompress the 
video capture card, or in a specialized encoding workstation used for capture and encod 
fi le that was used to compress it.
ing of real time (live live) streaming video. Encoding software, such as that included in 
the three major streaming architectures, provides codecs, as well.
Different codecs for different tasks
  the best way to learn to 
Video codecs and audio codecs work differently. You'll need to choose a video codec to 
compress your imagery, and an audio codec to compress your sound. And some codecs 
take advantage of these [different 
are more appropriate for certain kinds of work than others, since different codecs use 
codecs] is to play around with 
different compression strategies. The Adobe Premiere Technical Guides, which can be 
found in the Support area of the Adobe Web site at www.adobe.com, offer some more 
them. Take the same source clip, 
detailed descriptions of different types of compression and codecs.
run it through different codecs, 
Which streaming media codecs are available to you depends on which architecture(s) 
data rates, and frame rates, 
you choose. You'll fi nd some of the same codecs (MPEG 4, for example, for video; MP3, 
for example, for audio) in different architectures. But remember, since encoding not 
namic Medianamic Media
and carefully explore the 
yy
only compresses the fi le but also formats it for a specifi c architecture, even if the same 
results. This is still more of 
codec is used, streaming fi les are likely to play back only on the player that is part of 
the encoding architecture.
an art than a science. 
Currently, the three dominant architectures offer just a few options for streaming video 
obe Dobe D
 Ben Waggoner
codecs. While QuickTime provides some variety, RealNetworks and Windows Media  
dd
DV Web Video
48
AA
deliver little choice in codecs for streaming video. In terms of audio codecs, Real offers 
a wide variety of choices, with QuickTime 
32
32
47   Don't Be Scared of Bandwidth Math,  by Tim Kennedy, Streaming Media World,  May 26, 2000, http://smw.internet.com/symm/tutor/bandmath/index.html
48   Choosing a Streaming Video Technology,  by Ben Waggoner, DV Web Video, May 2000
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