[theora] Marketing stuff
maikmerten at gmx.net
Wed Sep 12 12:39:38 PDT 2007
Aaron Colwell schrieb:
> While I agree that human eyes are the best, PSNR even with all of its
> flaws has been commonly used
> in academic papers, codec evals, etc. to compare codec performance.
> While it isn't the best metric it
> is A metric that can be informative. I'd prefer some sort of
> double-blind human test, but obviously that
> is much more difficult to coordinate.
Something like http://www.cns.nyu.edu/~lcv/ssim/ , which introduces a
psychovisual model, may offer a good tradeoff between "we can't afford
real tests" and "PSNR isn't any good".
>> (no postprocessing applied, QCIF, 25 fps, ~130 kbps)
Actually the video is not QCIF but CIF, which is four times the number
of pixels coded. Sorry for this mistake.
> I'm also concerned with terms like "Extremely low bitrate", which
> apparently maps to ~130kbps in
> your mind. For someone like me who has spent quite a bit of time in the
> past with mobile & modem speed
> media delivery, this isn't "extremely low" at all. Info like frame-size,
> frame-rate, and bitrate are key to
> deciphering what "extremely low bitrate" really means in this context.
Well, I do consider 130 kbps at CIF and PAL framerate to be extremely low.
Scaled down to QCIF you end up being at modem-bitrates, especially when
decreasing the framerate (which may be necessary as artifacts are
becoming more dominant at low resolutions).
But right, for comparisons between codecs more information has to be
provided. Note, however, that the current loop-filter comparison image
is showing two different settings of Theora and isn't e.g. a MPEG-4.2
vs. Theora comparison. All I wanted to illustrate is how effective
in-loop deblocking can be, albeit even then more information can't hurt.
> Where is Theora's? What
> does it do well? Where does it tend to break down? What is the
> bitrate/quality tradeoff I have to make
> if I pick Theora over say MPEG4-Part 2? How good is it at hitting the
> target bitrate specified? These
> are all questions that content providers are going to want answers to
> when deciding whether Theora is
> the right codec for them.
Those indeed are the right questions to ask.
> My intent isn't just to complain here. I am willing to help if people
> decide they want to do this sort of analysis.
> This should be relatively easy to do with minor modifications to ffmpeg
> & ffmpeg2theora.
Your input is very much welcome, I didn't have the impression you wanted
to complain. Thanks for offering your help.
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