Re: [codec] Discussion around ITU LS

Anisse Taleb <> Mon, 12 September 2011 07:59 UTC

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Date: Mon, 12 Sep 2011 08:00:36 +0000
From: Anisse Taleb <>
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To: Jean-Marc Valin <>
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Thread-topic: [codec] Discussion around ITU LS
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Cc: Jonathan Rosenberg <>, "" <>
Subject: Re: [codec] Discussion around ITU LS
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Dear Jean Marc,

The issue is really to understand how the Opus codec is optimized for the internet. I was under the impression that a major argument for starting this work in IETF is to supply a codec that is optimized for use on the internet and therefore functionality that facilitates operation in an IP based transport would be defacto part of the codec distribution. 

The question of whether this is integrated in the decoder itself or outside the decoder (i.e. post-processing) depends mainly on the qualify and complexity of the two solution.  You seem to prefer the use of this feature as a post-processing stage to the audio output, would you like to elaborate why is this better than an integrated approach ? 

Regardless of whether this is implemented inside or outside the decoder (your preferred solution), I strongly believe that such a feature needs to be part of the code distribution.

Kind regards,

From: Jean-Marc Valin []
Sent: 08 September 2011 16:30
To: Anisse Taleb
Cc: Cullen Jennings; Jonathan Rosenberg;
Subject: Re: [codec] Discussion around ITU LS

Hi Anisse,

I agree that time stretching/shortening is a desirable feature. However,
I think in the case of Opus it is best implemented outside the decoder
using a good generic algorithm, rather than re-inventing the wheel. Of
course, if you think an integrated implementation would be better, you
are welcome submit a patch for it.



On 08/09/11 06:38 AM, Anisse Taleb wrote:
> Dear Jean Marc,
>>> Does the WG consider  time shortening / stretching functionality they
>>> would want to include in opus as a technique to use for PLC?
>> While time stretching/shortening is something that can be useful, I
>> don't think it's really necessary for a codec *specification*. In fact
>> even the PLC is provided only as an example.
> Quoting the requirements document RFC 6366:
> "  It is desirable for the reference implementation to provide a time stretching/shortening
>     implementation, although it should not be normative."
> While I agree that this is something that should be non-normative, such an integrated implementation
> would be an important feature for any codec deployed on the internet and really differentiate Opus wrt. "codecs" which are considered unsuitable for the internet.
> Kind regards,
> /Anisse