W3C home > Mailing lists > Public > public-webrtc@w3.org > June 2012

Re: Spec question: Using settings dictionaries instead of MediaConstraints

From: Harald Alvestrand <harald@alvestrand.no>
Date: Fri, 22 Jun 2012 19:03:26 +0200
Message-ID: <4FE4A55E.2030300@alvestrand.no>
To: public-webrtc@w3.org
On 06/22/2012 03:37 AM, Justin Uberti wrote:
>
>
> On Thu, Jun 21, 2012 at 6:42 PM, Cullen Jennings <fluffy@iii.ca 
> <mailto:fluffy@iii.ca>> wrote:
>
>
>     On Jun 20, 2012, at 9:21 , Harald Alvestrand wrote:
>
>     > On 06/19/2012 03:45 PM, Justin Uberti wrote:
>     >>
>     >>
>     >> On Tue, Jun 19, 2012 at 8:57 AM, Stefan Hakansson LK
>     <stefan.lk.hakansson@ericsson.com
>     <mailto:stefan.lk.hakansson@ericsson.com>>wrote:
>     >> On 06/19/2012 08:30 AM, Randell Jesup wrote:
>     >> On 6/18/2012 3:22 PM, Justin Uberti wrote:
>     >>
>     >>
>     >> On Mon, Jun 18, 2012 at 2:57 PM, Cullen Jennings (fluffy)
>     >> <fluffy@cisco.com
>     <mailto:fluffy@cisco.com><mailto:fluffy@cisco.com
>     <mailto:fluffy@cisco.com>>>  wrote:
>     >>
>     >>
>     >>     This seems like good proposal, one comment on a small detail.
>     >>
>     >>     On Jun 15, 2012, at 1:28 PM, Justin Uberti wrote:
>     >>
>     >> >  SessionDescriptionOptions.IncludeAudio = true/false // forces
>     >>     m=audio line to be included
>     >> >  SessionDescriptionOptions.IncludeVideo = true/false // forces
>     >>     m=video line to be included
>     >> >  SessionDescriptionOptions.UseVoiceActivityDetection = true/false
>     >>     // includes CN codecs if true
>     >>
>     >>     I think these three should be constraints, not settings
>     because a
>     >>     given browser may not support any of them.
>     >>
>     >>
>     >> Practically speaking, what does that mean for applications?
>     >>
>     >> I can conceive of a browser implementing audio but not video.
>      And a
>     >> gateway or other stand-alone WebRTC box/functionality might
>     include JS
>     >> and these JS apis for ease of programming (and might be
>     audio-only).
>     >> (I'd try to avoid it in production, probably, but even that
>     might not be
>     >> needed with modern JS JIT speed so long as it didn't have to
>     tear down
>     >> and restart all the time.)
>     >>
>     >> CN codecs: I dislike them anyways.  :-)  An implementation
>     definitely
>     >> could avoid including those.
>     >>
>     >> Many codecs have built in CN modes. I guess for those it is
>     more a question of being able to switch off the VAD.
>
>
>     I think we need to focus on VAD not CN. Note all the use cases
>     erased are about VAD not CN. Note the text in section 5.1 is only
>     about VAD and says
>
>     VoiceActivityDetection
>     This is a enum type constraint that can take the values "true" and
>     "false". The default is a non mandatory "true".
>
>     Many codecs and system are capable of detecting "silence" and
>     changing there behavior in this case by doing things such as not
>     transmitting any media. In many cases, such as when dealing with
>     sounds other than spoken voice or emergency calling, it is
>     desirable to be able to turn off this behavior. This constraints
>     allows the application to provide information about if it wishes
>     this type of processing enable or disabled.
>
>
> I understand what you are saying, but other than omitting "CN" from 
> the list of codecs, what other effect do you expect this constraint to 
> have on the generated SDP?

It might not even have that effect. The SDP would reasonably announce CN 
as long as the browser was able to receive it, because the other partner 
might want to use CN, or another track that was added later might set 
VAD to true even if the first track had it false.

The important setting would be that the codec is configured not to 
choose to generate silence on no-voice-activity; this is a pure 
sender-side decision.

              Harald
Received on Friday, 22 June 2012 17:04:04 UTC

This archive was generated by hypermail 2.3.1 : Monday, 23 October 2017 15:19:28 UTC