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

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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