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Re: Update of Doohickey/AddTrack proposal

From: Justin Uberti <juberti@google.com>
Date: Thu, 19 Dec 2013 10:25:23 -0800
Message-ID: <CAOJ7v-0C5a1th44pXRGeuFO8SPG0hKjjsPoiwuwvDaf4uUai2w@mail.gmail.com>
To: Adam Bergkvist <adam.bergkvist@ericsson.com>
Cc: "public-webrtc@w3.org" <public-webrtc@w3.org>
On Wed, Dec 18, 2013 at 11:07 PM, Adam Bergkvist <
adam.bergkvist@ericsson.com> wrote:

> Great. It's time to advance with this proposal.
>
>
> On 2013-12-19 04:35, Justin Uberti 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).
>>
>
> Do we need to have RTP in the names? I know that these names won't be used
> much in code, but we need to talk about them :) and, when we add the
> RTC-prefix the name will start with two acronyms (which isn't very nice
> IMO). Perhaps we could call them RTCMediaSender/RTCMediaReceiver? The
> network behavior is given by "sender"/"receiver" and "media" distinguish
> them from the data channel.


We've already got RTCIceXXXX, so this isn't really making things any worse.
I considered RTCTrackSender/Receiver, but went with RTCRtpSender in the
event that we ever wanted to support some other protocol (e.g. SCTP), which
would have its own sender/receiver objects.

If others strongly prefer RTCMediaSender, I could go along with that name
though.

>
>
>  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;
>>
>
> Nit: these need to be getter methods.


OK. getSenders() and getReceivers() it is.

>
>
>     EventHandler onaddtrack;  // replaces onaddstream; onremovestream is
>> not needed
>>
>
> I'm a bit confused by the comment above. Since we don't use streams here
> onremovestream goes away naturally, but did you mean that we don't need
> onremovetrack?


Yes. onremovetrack is much more easily accomplished by track.onended().

>
>
>  };
>>
>> 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.
>>
>>
> Diff of needed changes to our simple RTCPeerConnection example:
>
> --- a/webrtc_simple_example_old.js
> +++ b/webrtc_simple_example.js
> @@ -6,6 +6,9 @@ var pc;
>  function start() {
>      pc = new RTCPeerConnection(configuration);
>
> +    // used to render incoming tracks
> +    var receiveStream = new MediaStream();
> +
>      // send any ice candidates to the other peer
>      pc.onicecandidate = function (evt) {
>          if (evt.candidate)
> @@ -17,15 +20,20 @@ function start() {
>          pc.createOffer(localDescCreated, logError);
>      }
>
> -    // once remote stream arrives, show it in the remote video element
> -    pc.onaddstream = function (evt) {
> -        remoteView.src = URL.createObjectURL(evt.stream);
> +    // once remote media arrives, add it to a stream to be rendered
> +    pc.onaddtrack = function (evt) {
> +        receiveStream.addTrack(evt.receiver.track)

+
> +        if (!remoteView.srcObject)
> +            remoteView.srcObject = receiveStream;
>      };
>

The stream would still be generated and the track would be part of it, by
virtue of the MSID grouping. It's not necessary to create receiveStream or
do addTrack here.

>
> -    // get a local stream, show it in a self-view and add it to be sent
> +    // get a local stream, show it in a self-view and add the tracks to
> be sent
>      navigator.getUserMedia({ "audio": true, "video": true }, function
> (stream) {
>          selfView.src = URL.createObjectURL(stream);
> -        pc.addStream(stream);
> +
> +        stream.getAudioTracks().forEach(pc.addTrack);
> +        stream.getVideoTracks().forEach(pc.addTrack);
>      }, logError);
>  }
>
> /Adam
>
Received on Thursday, 19 December 2013 18:26:13 UTC

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