[theora] A comparison of VP3, and two MPEG-4 variants

Colin Mckellar blibblelibby at black-market-babies.com
Tue Mar 25 06:58:23 PST 2003

On Tuesday, March 25, 2003, at 01:42  AM, Marco Al wrote:

> 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?

I use a constant quantizer when possible.
Even though many people do not use constant quantizer when encoding, I 
think it is still relevant, as it gives the best over all quality that 
a codec can produce. A poor choice of settings can cripple the 
performance of most codecs, and skew any results. In my opinion, the 
best way to test competing codecs is to test them at their peak.

> 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).

I guess the approach of my test (I think that it has already been 
established that using psnr makes the conclusions less valid) is only 
applicable to non-streaming situations. Different tests based around 
streaming would be needed for that... Some codecs are very optimised 
for streaming (ZygoVideo comes to mind) at the expense of all else.


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