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Old 23rd December 2010, 21:11   #19  |  Link
*.mp4 guy
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Cqm's are useful for compensating for source oddities in general. And are pretty much required for compressing something that has been lowpassed, because a dct of a lowpassed image will still contain some high frequencies (some of which will be encoded, at pretty much any bitrate that looks decent) which contribute very very little to decode quality and nothing to decode detail levels.

Cqm's are also helpful for psyops in encoders that don't actively optimize for grain/detail retention at the quantization/rdo level, aq alone is not enough in some cases.

To expand on compensating for source oddities, for example sometimes a source is a bit soft (and that's how it is supposed to be, no lowpassing required), flat matrices often don't look that great in such situations.

I have to state that I don't use anything but hcenc anymore, and its quite possible that the way other encoders such as cce are set up, they don't get any benefit from matrices, there are plenty of ways this can happen that don't necessarily mean "matrices don't do anything useful".

Basically, cqm's are for making sure that you have a roughly equal amount of all of the undesirable artifact types in your output, and that you don't have one specific thing that jumps out as worse then everything else. Unsurprisingly, if you have a perfect source, and an encoder with aggressive psyops built in, cqm's are not terribly useful.
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