Linked by Brooss on Tue 15th Mar 2011 23:32 UTC
Benchmarks A comment on the recent article about the Bali release of Googles WebM tools (libvpx) claimed that one of the biggest problems facing the adoption of WebM video was the slow speed of the encoder as compared to x264. This article sets out to benchmark the encoder against x264 to see if this is indeed true and if so, how significant the speed difference really is.
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RE: Things we already knew about
by galvanash on Wed 16th Mar 2011 20:08 UTC in reply to "Things we already knew about"
galvanash
Member since:
2006-01-25

No, they're not. Just use a pixel difference utility and do it objectively. For my tests I use this: http://pdiff.sourceforge.net/


That is a great utility, but it has exactly the same problem as using PSNR for this kind of stuff... The fact that it uses perceptual biases instead of strict signal to noise doesn't matter much. The problem is both a utility like the one you use and PSNR is meant for comparing an input to an output. One measures SNR, the other perceptual differences in pixels. In either case you get a relative difference to the input, i.e. a "how much has changed" value.

Both are a fair facsimile of human vision, and arguably pdiff is a better one. Either metric tends to work decently at low compression ratios, but neither do a good job for comparing "subjective" video quality when you start dealing with high compression ratios where the output is often significantly different from the input.

The point is that being as close as possible to the input is not the goal at high compression ratios, it is more important to have the output look clean and natural, contain minimal artifacts, not lose too much "subjective" detail, etc.

Higher compression ratios (ratios that you as a video professional would outright reject because they adversely affect quality too much) are the norm for web video... PSNR and pdiff metrics for such video are mostly useless as you can easily find examples where the relative scores do not at all match most peoples subjective opinions.

Edited 2011-03-16 20:09 UTC

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