Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05

Paul Kyzivat <> Fri, 01 November 2013 22:49 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 3727C21E80B0 for <>; Fri, 1 Nov 2013 15:49:50 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -0.255
X-Spam-Status: No, score=-0.255 tagged_above=-999 required=5 tests=[AWL=0.182, BAYES_00=-2.599, FH_RELAY_NODNS=1.451, HELO_MISMATCH_NET=0.611, RDNS_NONE=0.1]
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id NFI0YLD4EKUn for <>; Fri, 1 Nov 2013 15:49:44 -0700 (PDT)
Received: from ( [IPv6:2001:558:fe14:43:76:96:62:48]) by (Postfix) with ESMTP id 10F4111E8136 for <>; Fri, 1 Nov 2013 15:49:40 -0700 (PDT)
Received: from ([]) by with comcast id kD5R1m00327AodY55NpgRZ; Fri, 01 Nov 2013 22:49:40 +0000
Received: from Paul-Kyzivats-MacBook-Pro.local ([]) by with comcast id kNpg1m00Q3ZTu2S3fNpg76; Fri, 01 Nov 2013 22:49:40 +0000
Message-ID: <>
Date: Fri, 01 Nov 2013 15:49:40 -0700
From: Paul Kyzivat <>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:24.0) Gecko/20100101 Thunderbird/24.1.0
MIME-Version: 1.0
To: Martin Thomson <>
References: <> <> <> <> <> <>
In-Reply-To: <>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=q20121106; t=1383346180; bh=kTHH98WCGlqQNynvotFY4zqStOYADBJtEHiH3Z3h7WI=; h=Received:Received:Message-ID:Date:From:MIME-Version:To:Subject: Content-Type; b=hMqQppKra6aAjdQSCFs3J267abHEIlReMVjotu8WuBNWMgFEAlDIh6r2CoxfsqMMd fvwnHtepDEAjg2pxmsTQ/uRL0IesEAkFS8VezWkpINjvcvE1nNqJdHeDo9kvCzseL9 YXvaHHi5dnNOi8Wt769qLwnUraz/vHf6HIp8na34V+ov+Yhk1LRvhdSxeaL5m/Ngk9 z5Bgr7KoHMwLMOi5yyUbkDoNeapgrEzOdRgjT9sHD7y28A9KZ/IHz+3oQNRQoXJegP h/I5ab4kOGGaPwukzO7pLCfsVvLf1m1o2sQluBCIm8VyUEd1StR3uBEbX/HRIPj3/n Vbq/DrOl9Ap4w==
Cc: "" <>
Subject: Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Real-Time Communication in WEB-browsers working group list <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Fri, 01 Nov 2013 22:49:50 -0000

On 11/1/13 2:10 PM, Martin Thomson wrote:
> On 1 November 2013 13:52, Paul Kyzivat <> wrote:
>> "MediaStreamTrack.readonly Read only
>>      Is a boolean value with a value of true if the track is readonly (such a
>> video file source or a camera that settings can't be modified), false
>> otherwise."
>> That seems to imply that one that isn't read-only must be read-write. I
>> don't see any mention of write-only.
> This attribute only really pertains to the constraints API, which is
> used to do things like switch cameras between capture modes.  This is
> to do things like change resolutions or capture rates on physical
> devices.  The assumption here is that this interface is not
> appropriate for tracks that originate from the network and so this is
> a clear signal to an application that trying to apply constraints is
> going to fail.

OK, so that doesn't mean what I thought it did. (Sorry, but I haven't 
been following the WebRTC API side of this.)

Looking at:

I don't find any notion of readonly or writeonly tracks. If you are 
going to use the presence of readoly and writeonly tracks to determine 
the directionality of the m-line, what property of the track determines 

> I know that this oversimplifies the process and that constraints could
> be used to provide indications back to RTCPeerConnection about what
> constraints to apply to its negotiation functions, but I think that
> the conclusion was that this was overcomplicating things.  And we know
> very well that it is already complicated beyond the comprehension of
> mere mortals anyway.

Its currently beyond my comprehension. Take that for what its worth.