[opus] Antw: Re: Antw: Re: Possible bug in Opus 1.3

Emily Bowman silverbacknet at gmail.com
Tue Nov 6 08:16:10 UTC 2018

On Mon, Nov 5, 2018 at 10:54 PM Ulrich Windl <
Ulrich.Windl at rz.uni-regensburg.de> wrote:

> >>> Emily Bowman <silverbacknet at gmail.com> schrieb am 05.11.2018 um 20:46
> in
> Nachricht
> >
> > As you've found, Opus is always 48kHz, never more, never less. Its
> > resampler is very accurate, and should never introduce noise.
> That's an interesting point: Why is that so? Couldn't the file size (and
> computing effort on encoding/decoding) be reduced when allowing different
> sample rates? Especially when the source has lower sampling rate, I wonder
> whether that isn't just a waste of bits...

It significantly simplifies the internal structure, the spec, the encoder,
and the decoder, without wasting any bits. OK, the collection of missing
bands generates one or two bits per frame, after entropy coding, but that's
not significant in any use case. Opus was specifically designed for this
scenario and aggressively optimizes it. If only 4kHz is in the input, only
4kHz will end up encoded, even if it's first upsampled to 48kHz.

Maybe there's some bug still undiscovered. Would you agree that Opus should
> encode a pure sinus tone efficiently? Or would it really prefer to encode
> white noise?

Whether efficiently encoding a continuously variable sine wave makes sense
is waaaaaay outside my wheelhouse. Jean-Marc or Monty should answer that. I
was just commenting on the fact that it probably needs to be re-runed at
this point.

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