Subject: Re: [AVT] Common Format: draft-ietf-avt-evrc-07, draft-mathai-avt-smv-00, Purevoice, etc.

From: Randall Gellens <[email-masked]>
Date: Tue, 04 Sep 2001 17:49:06 -0700

Is it useful to have a common format for EVRC and SMV and possibly other 
codecs?  This probably depends on sub-questions: Are there likely to be 
implementations which must support multiple codecs?  Is it simpler for such 
implementations if the formats are identical?

If it is useful to have a common format, is it harmful to have multiple 
formats for the same codec?  If so, we probably want to roll the current 
EVRC and SMV drafts into the new common one.

As for MIME registration, it occurs to me that we may be able to have one 
new MIME type for the common format, with a parameter specifying which 
particular codec is being used.  For example, "audio/foo; codec=bar".  The 
common format specification can include in the IANA Considerations section 
instructions on registering new values for the codec parameter for future 
codecs which want to use the common format.  Presumably such registration 
would include the mapping between frame type and frame length, which 
hopefully would be about the only difference from one codec to another.

Making EVRC and SMV use the same format is probably an easier question than 
including PureVoice as well, and so should be discussed separately, I think.

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
http://www1.ietf.org/mailman/listinfo/avt

---

From: Colin Perkins <[email-masked]>
Date: Tue, 04 Sep 2001 21:17:09 -0400

>EVRC and SMV drafts into the new common one.

If the codecs are sufficiently similar, it may make sense for the payload
formats to be similar. It's possible that they may be identical in some
cases (e.g. AMR and AMR-WB use the same format, even though they are
different codecs with different MIME types).

>hopefully would be about the only difference from one codec to another.

No! Each codec should have a separate MIME type, otherwise lots of things
will break...

Colin

---

From: Randall Gellens <[email-masked]>
Date: Wed, 05 Sep 2001 15:15:57 -0700

At 07:10 PM 8/30/2001 -0700, Adam Li wrote:
>I suppose it would not be too hard to have a common format that works for
>both EVRC and SMV. There is nothing in the current draft that is codec
>specific which would prevent this. It does reduce the complexities of
>protocols and implemenation.

Perhaps we should delay sending the EVRC draft to IETF last call while we 
consider a common format.

---

From: Pete McCann <[email-masked]>
Date: Fri, 7 Sep 2001 10:45:23 -0500

I do not think it is a good idea to merge the two specifications - as
we have been discussing off-list, there may be significant changes
required to the SMV draft to support the more complex rate-negotiation
required with SMV.

Let's keep the EVRC draft on the last-call track and get it finished.
These are really two different codecs and they deserve two different
specifications. 

-Pete

---

From: Randall Gellens <[email-masked]>
Date: Fri, 07 Sep 2001 13:58:10 -0700

>required to the SMV draft to support the more complex rate-negotiation

I wasn't aware of any off-list discussions regarding SMV.  (Until we saw 
the draft appear we were preparing our own SMV draft.)

>These are really two different codecs and they deserve two different

I can see enough advantages of a single implementation supporting both in 
an identical format that I'd prefer a little more time to explore the 
issues.  If it turns out that they really do need separate specifications, 
there will have been no harm in a small delay of EVRC.  If it turns out 
that a single format makes sense, it would be bad to already have a 
separate EVRC specification out there.

---

From: "Eric C. Rosen" <[email-masked]>
Date: Sun, 9 Sep 2001 18:23:57 -0700

At 13:58 -0700 9/7/01, Randall Gellens wrote:
>I wasn't aware of any off-list discussions regarding SMV.  (Until we 
>saw the draft appear we were preparing our own SMV draft.)
>
>I can see enough advantages of a single implementation supporting 
>both in an identical format that I'd prefer a little more time to 
>explore the issues.  If it turns out that they really do need 
>separate specifications, there will have been no harm in a small 
>delay of EVRC.  If it turns out that a single format makes sense, it 
>would be bad to already have a separate EVRC specification out there.
>

I agree with Randy's comments.

The similarity of the EVRC and SMV draft payload specifications to 
the original PureVoice payload specification suggests that a common 
specification for encapsulating these two wireless vocoders as well 
as potentially future wireless vocoders is possible.

We should at least explore the uitlity of a common payload 
specification that addresses the needs of:

- low data-rate
- variable rate
- frame based
- wireless vocoders

supporting

- interleaving
- bundling of multiple frames per datagram
- vocoder specific options (rate reduction, etc)

--Eric