Re: [MMUSIC] Towards Simulcast

Peter Thatcher <pthatcher@google.com> Sat, 17 October 2015 02:45 UTC

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From: Peter Thatcher <pthatcher@google.com>
Date: Fri, 16 Oct 2015 19:45:05 -0700
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To: Adam Roach <adam@nostrum.com>
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Cc: Adam Roach <abr@mozilla.com>, "mmusic@ietf.org" <mmusic@ietf.org>, Cullen Jennings <fluffy@iii.ca>
Subject: Re: [MMUSIC] Towards Simulcast
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On Fri, Oct 16, 2015 at 6:15 PM, Peter Thatcher <pthatcher@google.com>
wrote:

>
>
> On Fri, Oct 16, 2015 at 10:26 AM, Adam Roach <adam@nostrum.com> wrote:
>
>> Moving to MMUSIC
>>
>> On 10/16/15 11:59 AM, Peter Thatcher wrote:
>>
>> There's a lot of important stuff in the draft that wasn't discussed at
>> the interim call, such as the attributes/constraints an a RID and what's
>> mandatory to implement and not and how you know what the other side
>> supports or not.
>>
>>
>> So, let's step down from the meta-conversation and into the conversation,
>> then. Addressing these three points:
>>
>> There's a list of attributes in the current document. Do you think we
>> need additional ones? If so, which ones?
>>
>
> ​For the purposes of WebRTC, I think we need none of them, and should at
> most support max-br.  ​So I'd actually be in favor of removing attributes
> rather than adding them.  The fewer there are, the faster we can get the
> document done.
>
>
>>
>> As written, the document doesn't require support of any specific
>> attributes. Do you think we should add a list of some that should be MTI?
>> If so, propose a list.
>> ​
>>
>
> ​None is good.​  Can we make "pt=" optional as well?
>

​I
t appears this was updated in -01 as
​ being optional to offer.  But if offer doesn't contain "pt=" and the
answer adds "pt=" when it wasn't in the offer, does the offerer have to
honor it?  What if the offerer doesn't want to support that?​


>
>> ​
>>
>>
>> Section 7.1 bullet 4 proposes a way to find out what the other side
>> supports. Are there use cases you have in mind that it doesn't work with?
>>
>
> ​That could really use an example, because it's not very clear from
> reading the text.  Please tell me if my understanding is correct:
>
> If an offerer generates "a=rid:send X pt=*​", does that mean it supports
> none of the attributes?  Does it have to put "a=rid:send X pt=*​
> max-width=1000000000" to indicate it supports max-width but allows any
> value?
>

​I​
t appears this was updated in -01 as ​"a=rid:X send max-width".  I like it.
​ ​
We should a
​dd an​
example of
​its use (if there isn't one; did I miss it?)



>
> If an offerer generates "a=rid:send X pt=*​ max-width=1000000000" and the
> answerer doesn't support max-width, can it reply with  "a=rid:recv X
> pt=*"?  Because it says in the document currently 'In the case of a syntax
> error or an unsupported parameter, the "a=rid" line is removed.', which
> seems to indicate it has to remove the RID, even though it's a receiver
> that doesn't want to constrain the a=rid line any further.   Why does it
> have to remove the a=rid line?
>

​Even in -01 is still says "i
n the case of a syntax
​ ​
error or an unsupported parameter, the "a=rid" line is removed.
"​
​
​  Shouldn't we say that if a parameter is unsupported, the answer may
remove it?  ​



>
>
> If the end result is that the offerer can put "a=rid:send X" in offer and
> the answerer can put "a=rid:recv X" in the answer, then that would be
> great, because that's exactly what I think a WebRTC client should be able
> to do (use no rid-level attributes and no pt constraints).
>
​
It looks like we're already there in -01 for offering ​"a=rid:send X".

But it doesn't appear you can answer back "a=rid:recv X" to​ "a=rid:send X
max-height" , and it appears that you could respond with "a=rid:recv X
pt=100" to ​"a=rid:send X".

​


>
>
>
>
>
>
>
>>
>>
>> /a
>>
>
>