[MPlayer-users] one-pass encoding results better than two-pass

Jason Garrett-Glaser darkshikari at gmail.com
Fri Jan 9 02:39:53 CET 2009

> I did not care for those numbers printed by mencoder as I mentioned earlier.
>   But you bring up an interesting question: what exactly does mencoder
> report in the units kb/s?  How does that relate to the bitrate=3000 option I
> was passing to the codec?

The output kbps is the actual bitrate.  The 3000 is the target
bitrate.  One of the purposes of multi-pass encoding is to get a
bitrate closer to your target bitrate, hence why the second pass gave
more precise results.

> You may misspoke there, there is no logarithm in SSIM.  Maybe you thought of
> PSNR.  I guess that you may wanted to point out that SSIM is not linear (but
> that does not automatically mean it is logarithmic).  That point is well
> taken; it was only my gut feeling at that point that the gain in SSIM/PSNR is
> not justified by the file size increase.

You cannot fairly compare encodes at different bitrates.  This entire
thread consists of you doing this.  If you don't think the gain is
justified, lower your bitrate!

> I note that the above metrics are arithmetic/structural and not perception
> based (as the definition goes).  Correlation with perception makes them
> useful and I read that SSIM is the current favourite in that regard.  But
> lossy video compression quality measurement will never be as objective as say
> temperature measurement.

SSIM is not at all the favorite (there are many better ones, involving
frequency subbands mostly, and even in the category of SSIM there's
MS-SSIM or whatever it is), and is still a terrible metric.  It is
basically variance-weighted PSNR, nothing more.

I'm not going to bother anymore with someone who cannot listen to what
I say and insists on acting as if they know more about x264 than one
of its own developers.

Dark Shikari

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