Re: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization

On 2013-02-08 22:37, Harald Alvestrand wrote:
> On 02/07/2013 09:08 PM, Charles Eckel (eckelcu) wrote:
>>> -----Original Message-----
>>> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On
>>> Behalf Of Eric Rescorla
>>> Sent: Thursday, February 07, 2013 3:03 PM
>>> To: Stefan Hakansson LK
>>> Cc: rtcweb@ietf.org
>>> Subject: Re: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for
>>> synchronization
>>>
>>>
>>>
>>> On Thu, Feb 7, 2013 at 11:59 AM, Stefan Hakansson LK
>>> <stefan.lk.hakansson@ericsson.com> wrote:
>>>
>>>
>>>     On 02/07/2013 08:43 PM, Eric Rescorla wrote:
>>>
>>>
>>>
>>>
>>>
>>>
>>>             My question is basically: what if the sender creates two
>>>             MediaStreams for which all tracks have local sources
>>> (cam's,
>>>             mike's), sends them to a peer, will the RTP streams for
>>> both
>>>             MediaStreams have the same or different CNAME?
>>>
>>>             I argued for that they should have the same.
>>>
>>>
>>>         Yes, I think this is a separate (and fraught) question. :)
>>>
>>>
>>>
>>>     Separate question, but I think the answer should be documented
>>> (regardless on if it is "same", "different" or "implementers choice").
>>>
>>>
>>>
>>> Agreed.
>> I think SHOULD is the correct thing to document. I can imagine there
>> will be cases in which the sender will be a somewhat distributed app
>> that does not really know that the media source should be
>> synchronized, so it will assign a different CNAME.
>> The rest of the proposal sounded good as well.
>>
>>
> SHOULD often makes me unhappy, because it can lead easily to something
> being true so much of the time, people forget to check for whether it is
> true or not.
>
> I think "all the streams have local sources" is a property that we
> shouldn't require that one end of a PeerConnection reveals to the other
> end.

When you say "streams" above I guess you mean RTP streams (or 
MediaStreamTracks) as it would not make sense to make this a secret when 
they are transported in different MediaStreams but expose it if they are 
in the same.

What info would reveal this ("have local sources")? Is it them having 
the same CNAME?

>
> (Parenthesis: In the discussion, the question was raised of what it
> meant to send out two tracks in one MediaStream that were not
> originallly synchronized - one local and one remote, for instance. The
> best answer I heard was that they would have to be synchronized
> (re-clocked if necessary) in such a way that when played out at the
> recipient, they would give the same experience as when played out
> locally at the sender - same relative timing for the playout.)
>
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