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Re: Audio and Opus configurability for speed and quality (at the expense of bandwidth)

From: <piranna@gmail.com>
Date: Thu, 25 Jul 2013 10:20:51 +0200
Message-ID: <CAKfGGh26jdtL__1R1M50Nn8zYwY1Bg6=mkrgryGn20kUv4jNCw@mail.gmail.com>
To: tim panton <thp@westhawk.co.uk>
Cc: lonce <lonce.wyse@zwhome.org>, public-webrtc <public-webrtc@w3.org>
El 25/07/2013 10:19, "tim panton" <thp@westhawk.co.uk> escribió:

> When we started discussing the constraints API - this was an issue that
> came up,
> you would be able to mark an audio stream as 'for live music' and the
> codec params
> would be set accordingly. (low latency, high quality, no voice
> enhancement).
> Even though we have settled on Opus I think it would be a bad plan to
> expose the
> codec specific 'knobs'. Better to allow the developer to express their
> needs in more
> generic terms and have the browser interpret those needs in the context of
> the codec.
> (heck, it might decide to do lin16 at 48khz !)
> T.
> On 14 Jun 2013, at 08:41, lonce <lonce.wyse@zwhome.org> wrote:
> Hello -
>     I have a couple of questions I have not been able to answer myself
> after looking over published docs. I am interested in maximum speed and
> uncompromised quality transmission (for musical purposes), which leads to
> these questions:
> 1) What exactly is the strategy of the "components to conceal packet
> loss".  Is there a strategy specifically for audio packet loss?
> 2) Can the audio echo cancellation (AEC), automatic gain control (AGC),
> and noise reduction, be turned off (not used)?
> 3) Can compression by turned off completely (to avoid the algorithmic
> delay of coding/endcoding)?
> 4)  If you cannot bypass the compression algorithm, what is the minimum
> delay one can achieve?  It appears to me (from
> http://www.webrtc.org/reference/architecture and
> http://en.wikipedia.org/wiki/Opus_%28codec%29 ) that analysis frame sizes
> down to 2.5ms (CELT layer) and 10ms (SILK layer) are possible. This, in
> addition to "look ahead"  and algorithm delay puts the minimum delay at at
> least 20 ms, right?
> 5) Does one have control over how many analysis frames are sent per packet
> (could I set it to 1)?
> Musicians have been using a system called JackTrip (CCRMA, Stanford
> University) which suuports uncompressed transmission, and sub-millisecond
> frames (and packet) size. To recover from UDP losses, it sends redundant
> streams, and the receiver takes the first packet that arrives with the time
> stamp it needs next to reconstruct the audio on the receiver. My questions
> above are all about how close WebRTC can come to achieving the same
> performance.
> Thanks!
>                  - lonce
Received on Thursday, 25 July 2013 08:21:19 UTC

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