[theora] A comparison of VP3, and two MPEG-4 variants
dan at on2.com
Mon Mar 24 09:56:33 PST 2003
good points, but I think constant Q is pretty much the standard for VBR/storage type applications. Doesn't Vorbis basically use a constant Q model for the most part?
it's only when you have hard limits on transmission speeds that you need to employ rate control algorithms that vary Q over time.
___ Dan Miller
(++,) Founder, CTO, On2 Technologies
<p>> -----Original Message-----
> From: Marco Al [mailto:marco at simplex.nl]
> Sent: Monday, March 24, 2003 12:43 PM
> To: theora at xiph.org
> Subject: Re: [theora] A comparison of VP3, and two MPEG-4 variants
> From: "Freun Laven" <FreunLaven at earthlink.net>
> > >I think you would be much better off relying on subjective
> > >measurements rather than PSNR.
> > Considering the incredible vaguness in what's considered
> "good enough",
> > any decent testing method is going to *have* to do some sort of
> > objective, reproducable measurments. (Unless, of course, people are
> > going to be satisified with some group of 'experts' making
> > of what is 'best'.)
> Not from a group of experts, but a group of layman yes.
> Experts can have
> preconceptions based on objective measures and can tie them
> to specific
> codecs by recognising specific artifacts.
> MOS is the benchmark to which all objective measures are
> compared. To any
> individual his subjective measure is the only one which
> counts ... how then
> can you look at the big picture and declare subjective
> measures meaningless?
> Obviously the average subjective impression is the only
> measure which has
> any meaning at all ...
> > With video it's even worse. And for somebody like myself, who has
> > eyesight problems, what I would consider to be 'good' would
> probably be
> > laughed at by others, simply because I have trouble
> detecting the subtle
> > differences.
> That is a rather extreme example, on average over all
> potential users these
> kind of things even out. Although since with subjective tests
> you usually
> have a rather small group your opinion would indeed probably
> not be usefull
> to include :/
> > A purely subjective comparison is worthless.
> Actually it is the only comparison of value :) Indeed, the value of
> objective measures themselves is measured by how well they
> correlate with
> subjective scores.
> On a related matter, I dont quite see the relevance of
> constant quantizer
> measurements ... they are usefull as micro benchmarks during codec
> development to compare a codec against its previous version,
> but does anyone
> actually use constant quantizer encoding in practice? If not
> how are the
> results relevant for comparing codecs against eachother?
> Id find the results more relevant if the codecs were compared
> as they would
> be used. Which means seperate tests for streaming (CBR/ABR)
> and storage
> applications (VBR/2-pass encoding if available ... CBR/ABR
> coding with the
> rate set to what is needed for the required size if not).
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