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Re: Update of Doohickey/AddTrack proposal

From: Martin Thomson <martin.thomson@gmail.com>
Date: Thu, 19 Dec 2013 10:12:28 -0800
Message-ID: <CABkgnnXCCQHtnEco_szqcVuQKLKYSC1PG-wuSqT_3dLcBkz2DA@mail.gmail.com>
To: Justin Uberti <juberti@google.com>
Cc: "public-webrtc@w3.org" <public-webrtc@w3.org>
I think that you need to talk a little bit about how you plan to
manage the difference between send and receive tracks.

The onaddtrack (which I think would be even clearer as onremotetrack)
needs a description of its arguments.  I think that those should be:

interface RemoteTrackEvent : Event {
  readonly attribute RtpReceiver receiver;
  readonly attribute MediaStreamTrack track;
  readonly attribute MediaStream[] streams;
};

The stream here is important.  This makes onaddstream polyfill
actually possible.  It's otherwise impossible to learn what stream is
being sent.  The fact that a single track can be part of multiple
streams means that you need this to be cardinality n.

On 18 December 2013 19:35, Justin Uberti <juberti@google.com> wrote:
> Based on some feedback I've received, I've slightly updated my proposal
> (originally inspired by Martin) on doohickeys and replacing AddStream with
> AddTrack. See below:
>
> ------------------------------------------------------------------------
>
> I suggest we call the SendDoohickeys RtpSenders and the corresponding
> receive-side objects RtpReceivers. These objects allow control of how a
> MediaStreamTrack is encoded and sent on the wire, including "hold" state,
> prioritization, and multiple encodings (e.g. simulcast).
>
> You get a RtpSender as a return value from AddTrack (which replaces
> AddStream). You get a RtpReceiver as an argument to the new onaddtrack
> callback (which replaces onaddstream). The actual track object can be
> obtained as a property from the RtpReceiver (see below).
>
> For getting access to ICE/DTLS info, both RtpSenders and RtpReceivers can
> also have a reference to a DtlsTransport object, which will have its own
> state variables, including the RTCIceConnectionState of that particular
> transport, and the .remoteCertificates for the DTLS connection. This allows
> applications to monitor the state of individual transports, as well as
> inspect the certificates for individual transports.
>
> The actual interface is as follows:
>
> interface DtlsTransport {
>   attribute RTCIceConnectionState state;
>   attribute sequence<ArrayBuffer> remoteCertificates;
>   //... more stuff as needed
> };
>
> interface RtpSender {
>   readonly attribute MediaStreamTrack track;
>   readonly attribute DtlsTransport transport;
>   // various tweakable attributes
>   attribute bool active;  // controls "am I sending RTP"
>   attribute PriorityLevel priority;  // for relative bandwidth allocation
>   // for multiple encodings: simulcast (audio or video), layered coding
>   // specify the codec to use, resolution, bitrate, and any dependencies for
> each encoding
>   attribute sequence<EncodingParams> encodings;
> };
>
> interface RtpReceiver {
>   readonly attribute Transport transport;
>   readonly attribute MediaStreamTrack track;
>   // more stuff as needed
> };
>
> partial interface PeerConnection {
>   RtpSender addTrack(MST);  // replaces addStream
>   void removeTrack(RtpSender);  // replaces removeStream
>   readonly attribute sequence<RtpSender> senders;
>   readonly attribute sequence<RtpReceiver> receivers;
>   EventHandler onaddtrack;  // replaces onaddstream; onremovestream is not
> needed
> };
>
> For backcompat, addStream, removeStream, getLocalStreams, getRemoteStreams,
> and onaddstream can be trivially polyfilled in JS, so there is minimal
> impact on current applications.
>
> All together, the pipeline looks like this:
>
> Source ---> MST ---> RtpSender ---> Transport ---> (The Internet) --->
> Transport ---> RtpReceiver ---> MST ---> <video/>
>
> Each RtpSender/Receiver references a single MST, although a single
> RtpSender/Receiver can send/receive multiple encodings (e.g. simulcast).
> There are N RtpSenders/Receivers per Transport; N is controlled by the
> policy specified for BUNDLE.
>
Received on Thursday, 19 December 2013 18:12:55 UTC

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