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Opus encoder with "q" setting?
radorn
post Dec 15 2012, 01:13
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Well, title pretty much says it all.
Is there any such encoder or plans for it?
I was surprised opusenc doesn't have it, since vorbis had it even in the RC releases.
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radorn
post Dec 16 2012, 01:03
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Well, this is just user perception, but I thought the "quality" settings in modern codecs (wether it is audio or video) was an attempt to achieve a certain level of perceptual transparency where the actual bitrate is dependent on the variable complexity of the input without much constraint. Of course this results in a file where bitrate is variable, but from what I can grasp, a bitrate setting within a VBR "constraint" tries to sort of match the given bitrate as average instead of a given level of transparency, which is what I always thought vorbis did... So if you tell it to average to +/-96kbit it will depend on the complexity of the input how much perceptual quality the encoder can squeeze out of that given bitrate averaged, right?

What I always understood as a "q" setting is, in resume, a -more or less accurate- gauge of perceptual transparency, and the encoder is in charge of deciding just how much bitrate it needs to achieve it. but perhaps I was wrong...

This post has been edited by radorn: Dec 16 2012, 01:06
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Garf
post Dec 18 2012, 16:59
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QUOTE (radorn @ Dec 16 2012, 01:03) *
Well, this is just user perception, but I thought the "quality" settings in modern codecs (wether it is audio or video) was an attempt to achieve a certain level of perceptual transparency where the actual bitrate is dependent on the variable complexity of the input without much constraint.


Correct.

QUOTE
Of course this results in a file where bitrate is variable, but from what I can grasp, a bitrate setting within a VBR "constraint" tries to sort of match the given bitrate as average instead of a given level of transparency, which is what I always thought vorbis did...


Not correct. Vorbis remaps the bitrate your select to a quality level that *probably* works out approximately to what you selected.

QUOTE
So if you tell it to average to +/-96kbit it will depend on the complexity of the input how much perceptual quality the encoder can squeeze out of that given bitrate averaged, right?


Not correct (for Vorbis and Opus). The real bitrate that your clip gets will change, not the quality.

Vorbis and Opus *can* enforce the bitrate rigidly if you so desire, but this requires extra settings (--managed in Vorbis, --cvbr or --cbr in Opus). By default they do *not* do this, and there is no guarantee you end up with the bitrate requested. But we know that, over a large collection of music, it will work out to that on *average*.

Vorbis and Opus default to quality-based encoding (instead of enforcing the bitrate) because this is generally what you want anyway.
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