[MEncoder-users] Codec-independant objective quality measurement

Nicolas George nicolas.george at ens.fr
Wed Aug 2 12:53:54 CEST 2006

I am looking for a tool (Open Source and command-line, for Unix; I have
found MSU Video Quality Measurement Tool on the web, but it is neither) to
evaluate the quality of a video encoding.

I know the PSNR option of some codecs, and I use it a lot to evaluate the
effect of fine encoding options. But it is not satisfactory or the big

- I am not sure whether different codecs evaluate it exactly the same way.
  And even if they do, they do not display it the same way, and it is not
  always easy to know which part of the final statistic of one codec should
  be compared to which part for another codec.

- Codecs evaluate their PSNR with regard to the frame that is given to them,
  disregarding the effect of upstream video filters. That is especially true
  for scaling: if I downscale a video to 32x24, I can get lossless quality
  at less than 300 kbit/s, and the codec will tell me an infinite PSNR. But
  that does not mean that the result is perfect with regard to the original
  content. That example is exaggerated, but it would be nice to be able to
  evaluate whether, at a given bitrate, is is better to keep the original
  resolution or to downscale a little.

- PSNR is just one measure of video quality encoding. There are others
  metrics that may give a better evaluation of the subjective feeling of

So, I am looking for a tool to make such quality evaluations.

I wonder whether the best place for such a tool would not be inside mencoder
itself, tapping directly the decoded input frame and the output data.

An external tool would need to know all mplayer's video filters, because,
contrary to downscaling, I do not want the changes brought by cropping,
contrast change or deinterleaving taken into account negatively in the

Furthermore, an external tool may have problems to achieve exact match
between source and target frames, especially when seeking before the start,
while mencoder knows exactly which frame is which.

On the other hand, there are codecs that mencoder does not know (yet?) and I
wish I would be able to evaluate too, especially Theora. Anyway, there is no
such thing in mencoder at this time.

Does anyone know about a tool I could use?


  Nicolas George
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