Re: codec

Dennis J. Streveler (
Tue, 11 Jun 1996 12:37:42 -0700

At 02:36 PM 6/11/96 -0400, David I. Sommers, Ph.D. wrote:
>A codec is the software algorithm for "compressing-decompressing" a lot of
>information. The compressed data is sent in packets, through cyberspace and
>decompressed on the receiving end. Some codecs seem to work better than
>others - I wonder why?
>David Sommers

Oh David, there are HUGE differences in the competency, reliability of
different codecs.

For example, consider a video input. It might contain a more or less stable
image (a talking head) or a very dynamic image (say, an image of a slowly
rotating propeller blade). Some codecs work well on one, some on another.
Some codecs work well where speed is at a premium, others work best where
visual quality is at a premium. And so on...

I think the state of the art audio codecs can be found using Iphone, for
example. It is obvious that their (audio) technology is far superior to the
(audio) codecs found in ECU. A lot of work has been done in "speech
compression" these days, so this field has moved along rapidly. And codecs
can and have rapidly become obsolete and replaced by improved ones.

In the video field, I like to compare FreeVue's approach to video
compression to that used by ECU. With FreeVue when there is a lot of motion
in the image, the resolution gets grainer, giving it an "interlaced"
appearance like the interlaced gifs you see in your web browser. As the
image settles down, the resolution is increased, and the image looks less
grainy. With ECU, "blocks" of pixels are apparently updated, with the
resolution remaining constant. Two different approaches and methods to send
"too much" information down a "thin" and rather unpredictable pipe, i.e. the
Internet of today. Both have advantages and both disadvantages, as is almost
always the case in Computer Science alternative approaches.


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