[M4IF Technotes] Average compression

[Ben Waggoner]

on 11/29/02 10:06, Roland Bengtsson at d98rolb   stud.hh.se wrote:
> I wonder how much compression MPEG-4 can achieve. Of course this is a very
> general questions and the compression depends on many things like the
> movie, tha algorithm that is used etc. But I still want to know: I have
> seen a number around 17x compression.

    I've certainly had useable output at much, much higher rates than that
(beyond 100x compared to the uncompressed 4:2:0 source at the same
resolution).
    The real question isn't how low you can go, but how low you can go with
"good enough" quality, where "good enough" varies a lot from case to case.
> Maybe there is some documentation or paper that I can read further about
> this subject?
> 
> Here's my thought of the factors that may affect the compression:
> 
> The movie, is it slow or a action movie?

    Major effect.  Maybe 5x or more between the easiest and hardest kinds of
typical content.
> The algorithm for encoding, I would like to hear some numbers about the new
> H.26L/AVC algorithm.

    The profile matters a lot, and different encoders targeting the same
profile can vary by at least 3x.
> What profile is used, for example how effective is FGS against simple profile?

    Significant factor.
> The cpu-power available, this is of course important. Generally harder
> compression require more MIPS.

    Significant.  Doesn't matter much with offline encodes, since it just
goes slower, but real-time encoders may have to make sacrifices in quality
in order to be real-time.  Also, they can't do 2-pass.
> The amount of error-correction, have the medium for transport of the movie
> hight biterror rate?

    Slight effect at most.  But the profiles chosen for lossy environments
like FGS may be less efficient than those chosen for lossless environments.
Ben Waggoner <http://www.benwaggoner.com>
Compressed Video Consulting, Training, and Encoding
My Book:            http://www.benwaggoner.com/books.htm
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