Re: [codec] #28: Layered bit-stream

"Dmitry Yudin" <Yudin@spiritdsp.com> Thu, 06 May 2010 09:45 UTC

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From: Dmitry Yudin <Yudin@spiritdsp.com>
To: Christian Hoene <hoene@uni-tuebingen.de>, Vladimir Sviridenko <vladimirs@spiritdsp.com>, codec-bounces@ietf.org
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Cc: Slava Borilin <Borilin@spiritdsp.com>, codec@ietf.org
Subject: Re: [codec] #28: Layered bit-stream
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Hi Christian,

>From application point of view, the layered stream structure allows
server manipulate channel bandwidth individually for each user with zero
performance overhead. Obviously, conferencing is the most important
use-case. 

> a) First, this use case is a local optimization only. Thus, the must
not be standardized.
What do you mean exactly? "local optimization" of what?

> b) Second, instead of layered coding one can use other ways of
tweaking the implementation 
> performance. For example, if you calculate a 512 FFT do get two 256
FFTs for free. 
> I bet there are thousand other shortcuts which I am not aware of.
How do this interrelates with scalability? Please, explain.

Let's return back to the subject:
    Shall layered coding be supported? - we think "yes", because ...
(see my first sentence)
    Who needs it?                      - answered
    Can we drop this requirement?      - only if we have real good
reasons for it. Do we have them? 

Best regards,
Dmitry

-----Original Message-----
From: Christian Hoene [mailto:hoene@uni-tuebingen.de] 
Sent: Wednesday, May 05, 2010 11:02 PM
To: Vladimir Sviridenko; codec-bounces@ietf.org
Cc: Slava Borilin; Dmitry Yudin; codec@ietf.org
Subject: RE: [codec] #28: Layered bit-stream

Hi Vladimir,

>2/ we think that VoIP and Videoconferencing systems are users of such
>codecs.

Could you please explain your position a bit?

As far as I understand, layered coding helps if multiple streams having
the sample content but different rates must be generated.
For example, if a conferencing system stream the same audio stream to N
users but each users has a different bandwidth. Just encode
all layers and drop the higher layers for the low bandwidth users. This
approach is easy and efficient and reduce the encoding
complexity.

The arguments against are simple. 
a) First, this use case is a local optimization only. Thus, the must not
be standardized.
b) Second, instead of layered coding one can use other ways of tweaking
the implementation performance. For example, if you
calculate a 512 FFT do get two 256 FFTs for free. I bet there are
thousand other shortcuts which I am not aware of.

Thus, I have the opinion that layered coding is not worth the extra
bandwidth of 20 or more percentage. It is just good locally but
not needed for interoperability.

Yours,

 Christian






>Yours,
>Vladimir Sviridenko
>SPIRIT
>
>-----Original Message-----
>From: codec-bounces@ietf.org [mailto:codec-bounces@ietf.org] On Behalf
>Of codec issue tracker
>Sent: Sunday, May 02, 2010 5:10 PM
>To: hoene@uni-tuebingen.de
>Cc: codec@ietf.org
>Subject: [codec] #28: Layered bit-stream
>
>#28: Layered bit-stream
>------------------------------------+----------------------------------
-
>----
> Reporter:  hoene@...                 |       Owner:
>     Type:  defect                  |      Status:  new
> Priority:  minor                   |   Milestone:
>Component:  requirements            |     Version:
> Severity:  Active WG Document      |    Keywords:
>------------------------------------+----------------------------------
-
>----
> Shall layered coding be supported?
> Who needs it?
> Can we drop this requirement?
>
>--
>Ticket URL: <http://trac.tools.ietf.org/wg/codec/trac/ticket/28>
>codec <http://tools.ietf.org/codec/>
>
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