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

Martin Thomson <> Fri, 01 November 2013 21:10 UTC

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Date: Fri, 1 Nov 2013 14:10:39 -0700
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From: Martin Thomson <>
To: Paul Kyzivat <>
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Subject: Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05
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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.

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.