"Encoding Efficiency" Definition

Steve Underwood <steveu@dis.org> writes:

> Randy Yates wrote:
>> Hi Folks,
>> I scoured Google and believe it or not couldn't come up with
>> a definition of "encoding efficiency" (or coding efficiency)
>> in the context of video and audio codecs (MPEG4-AAC/LC, e.g.).
>> It seems to me the obvious definition is
>>  k = 1 - (output bitrate) / (input bitrate)
>> Is this reasonable? Does anyone know of anything
>> better, or can you suggest something better?
>
> If you think that is reasonable, it seems to follow that you must
> think it reasonable that selecting the poorest quality option for the
> codec is more efficient than selecting the highest quality
> option. 

I mentioned in an adjacent post to Allan that I had intended to report
the output quality along with this measure, so I wasn't ignoring the
interaction between the two. You probably posted this before my post
reached you.

> Most opinions of codec efficiency weigh heavily on the quality
> of the results, and that can be very subjective. Codec performance
> measurement is good a subject for starting a fight. :-)

Call me an agent provocateur, then... :)
-- 
%  Randy Yates                  % "Maybe one day I'll feel her cold embrace,
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%%%% <yates@ieee.org>           %        'Yours Truly, 2095', *Time*, ELO   
http://home.earthlink.net/~yatescr

The problem, as you note later, is that we normally specify the
compression ratio (output bitrate versus input bitrate) and test the
subjective quality of what comes out. So any codec can give a
compression ratio but not all give the same 'quality'.

The quality is subjective, and also depends on the purpose of the
listening/viewing and the ability of the listener/viewer to discern
differences. Great topic for long and meaningful discussions, bringing
in all those human touches like how we hear, see and feel. But less
easy to measure. :-)

Stefan Winkler - http://stefan.winkler.net/quality.html - discusses
ways to measure video quality quantitatively without subjective tests.
He also recently published a good book on the topic.

It isn't easy but it is a useful discussion. The idea being to try to
clarify what you mean by 'quality' and on what content under what
conditions, then find ways to quantify that and test it objectively.

Chris
=================
Chris Bore
BORES Signal Processing
www.bores.com

"Chris Bore" <chris.bore@gmail.com> writes:
> [...]

Thanks for your thoughts, Chris. I also apprecate the references
to Winkler's work.

--Randy


-- 
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