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

A couple of observations on this

(a) I agree with Christian that layered codecs usually need higher bitrates
to achieve the same quality. Of course we do want good quality over our
desired bitrate range, and it is likely to be more difficult to achieve that
with a layered codec.

(b) I agree with Dimity that layered codecs reduce the complexity of VOIP
gateways and perhaps conference bridges.  Also, with layered codec designs
you get wire-speed management of channel bandwidth, so there can be a delay
benefit as well as a complexity reduction.

(c) Arguing about the relative priority of multipoint conferences vs point
to point calls is pointless, because they are clearly both MUSTS.

I am not sure if Christian is arguing that layered codecs SHALL NOT be
considered, or if the requirements allow but are not biased towards layered
proposals.  If might be useful to clarify this point.

Stephen Botzko

On Thu, May 6, 2010 at 9:13 AM, Christian Hoene <hoene@uni-tuebingen.de>wrote:

> Hi Dimitry,
>
> >Hi Christian,
> >
> >From application point of view, the layered stream structure allows
> >server manipulate channel bandwidth individually for each user with zero
> >performance overhead.
>
> I understand. Because you as an application programmer want to have an easy
> life, the codec designer shall develop a more
> complicated codec? In addition, everybody should suffer from a higher bit
> rate? No, that is not fair.
>
> > Obviously, conferencing is the most important use-case.
>
> No, end-to-end connections are more frequent than conference calls.
>
> >
> >> 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?
>
> I mean that the layered coding is only used within one computer. It is not
> important in-between computers. And, it is only a
> performance optimization that make the conference gateway faster.
>
> Sincerely,
>
>  Christian
>
>
> >
> >> 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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> >>codec mailing list
> >>codec@ietf.org
> >>https://www.ietf.org/mailman/listinfo/codec
>
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