[FFmpeg-devel] Testing Inexact Data

Rich Felker dalias
Wed Jan 23 07:00:28 CET 2008

On Tue, Jan 22, 2008 at 09:38:24PM -0800, Mike Melanson wrote:
> Hi,
> I am at the point with the FATE server ( http://fate.multimedia.cx/ ) 
> where I want to start testing data that is not defined to be bit exact. 
> Michael recommended that I should use the tiny_psnr utility. Sounds 
> great, except that, well... I'm not very good at math and I don't know 
> what the numbers actually mean. :)
> I decoded surge-2-16-B-.mp3.mov from:
>    http://samples.mplayerhq.hu/mov/qtaudio/
> I decoded the file to WAV on x86_32 and PPC machines and then ran:
> $ tiny_psnr mp3-ppc.wav mp3-x86.wav 2 0 0
> stddev:  0.53 PSNR:101.81 bytes:2322432
> When I compare one of the files against itself:
> stddev:  0.00 PSNR:99.99 bytes:2322432

The 99.99 is probably a dummy number since the actual PSNR should be
infinity. No idea why it would be dummied out since infinity
computations with floating point numbers work just fine... oh,
tiny_psnr is all arcane fixed point code.. :) In that case, it'll take
a little bit of reading to interpret the numbers, I think. PSNR is
normally expressed in decibels but I think this is using some base-2
or base-16 thing...?


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