[opus] opusenc constant quality setting

[Larry Fenske]

Thanks, Gregory.  That's perfect, exactly what I wanted to know.

- Larry

On Thu, Nov 6, 2014 at 2:06 PM, Gregory Maxwell <gmaxwell at gmail.com> wrote:

> On Thu, Nov 6, 2014 at 8:55 PM, Larry Fenske <opus at towanda.com> wrote:
> > I'm a bit confused about VBR with Opus.  I see that the default is VBR,
> > but I don't see any way to specify a quality setting.  I can set a
> > target bitrate, but that's definitely not what I want; I want a constant
> > quality level, like "-q" in oggenc, and for the encoder to select
> > bitrates based on the desired quality.
> >
> > For example, for playback through earbuds or laptop speakers, I wouldn't
> > need anything better than low quality; through good headphones or decent
> > stereo speakers, medium quality; and for playback through $5000
> > speakers, high quality.  Bitrate is not relevant in these cases, except
> > I don't want the file to be larger than necessary for the desired
> quality.
>
> The VBR settings are 'constant quality'.  Bitrate is just used as a
> real-world unit indexed against a large corpus of diverse content.
> E.g. bitrate 128 is the quality that got the average rate for the
> whole corpus to 128.
>
> This avoids problems with an opaque quality setting having no external
> meaning (and drifting over time and/or having to add crazy values like
> -2 later ) and only making sense relative to itself.
>
> If you'd like, you can just imagine that the bitrate numbers in VBR
> mode are "quality" scaled by a somewhat funny 512kbit/sec/channel.
>
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