[XviD-devel] Qpel Problem Samples

[Christoph Lampert]

Hi,

thanks for the samples and detailed description. We'll check... So far we
know that _if_ Qpel is helpful, it already better for any short parts
of the video, and usually not by higher PSNR, but by lower filesize. 
So if you want to decide on QPel/noQPel you can encode a
short piece (10s) from the middle with fixed quant and then decide on
QPel/noQpel by smaller filesize. 

Maybe somebody could add such a feature the GUI? An "Auto" setting
for QPel?  Because MPEG-4 doesn't permit to just switch QPel on or off
within a clip.

gruel




On Thu, 4 Sep 2003 j_coleman at shaw.ca wrote:
> It was mentioned on the doom9 forums by Isibaar that if we came across some 
> samples where qpel performed worse than half pixel (ie lower PSNR) that we 
> could put them online and post a link.  I posted this on doom9 but I don't 
> know if any of you guys have seen it yet.  So anyway here are the source 
> files that I have found that when encoded with qpel exhibit a lower PSNR.  
> Probably though I should say something about how they were encoded first.  
> All three files were force-filmed to 23.976fps in dvd2avi and this avs script 
> was used or something similar: 
> 
> LoadPlugin("C:\Program Files\Avisynth 2.5\plugins\Mpeg2dec3.dll")
> Mpeg2Source("C:\TERMSE_SIDEA\VIDEO_TS\terminatortest.d2v")
> 
> They were then loaded into virtualdubmod and encoded with a dev-api-4 build 
> from August 19th built with ICL7.0 just a win32 release, only default options 
> were used except of course for qpel.  All encodes were two pass and PSNR 
> measurements were performed with psnr4avi.  Anyways here are the results:
> 
> For a short clip aiming for 2MB:
> with qpel: Average PSNR (Y U V): 43.26, 45.70, 45.76 Average PSNR: 44.91
> without qpel: Average PSNR (Y U V): 44.18, 45.86, 45.96 Average PSNR: 45.33
> And here is the url for the source file http://www.geocities.com/bonzi5252/..
> .atorsample2.zip
> 
> For another short clip again aiming for 2MB:
> with qpel: Average PSNR (Y U V): 44.15, 48.54, 49.01 Average PSNR: 47.23
> without qpel: Average PSNR (Y U V): 45.15, 48.67, 49.13 Average PSNR: 47.65
> Source file can be found here http://www.geocities.com/bonzi5252/bondsample.
> zip
> 
> And one more clip aiming for 350KB:
> With qpel: Average PSNR (Y U V): 45.26, 48.94, 49.09 Total Average PSNR: 47.
> 76
> without qpel: Average PSNR (Y U V): 45.94, 48.98, 49.14 Total Average PSNR: 
> 48.02
> And the source file http://www.geocities.com/bonzi5252/bondsample2.zip
> 
> If you need more samples or if these ones are completely useless, don't 
> hesitate to ask or comment.
> 
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