Add document for simulcast (#298)

* Add document for simulcast

* Update some comments

* Change some descriptions

* Rewrite some descriptions

Author: starwarfan

docs/jsdoc/config.json

@@ -3,7 +3,7 @@
   "recurseDepth": 10,
   "source": {
     "include": "src/sdk",
-    "exclude": ["src/sdk/rest", "src/sdk/nuve", "src/sdk/ui"],
+    "exclude": ["src/sdk/rest", "src/sdk/ui"],
     "excludePattern": "w*.legacy.*"
   },
   "sourceType": "module",

docs/mdfiles/simulcast.md

@@ -0,0 +1,73 @@
+OWT Simulcast Description
+---------------------
+
+# {#simulcast}
+The conference server supports simulcast. This can be enabled through OWT Client SDK for JavaScript.
+
+1. Publish a simulcast stream
+~~~~~~{.js}
+// Example of simulcast publication.
+conference = new Owt.Conference.ConferenceClient();
+// ...
+conference.join(token).then(resp => {
+    // ...
+    Owt.Base.MediaStreamFactory.createMediaStream(new Owt.Base.StreamConstraints(
+            audioConstraints, videoConstraints)).then(stream => {
+        /*
+         * Use `RTCRtpEncodingParameters` as publish option
+         * (https://w3c.github.io/webrtc-pc/#dom-rtcrtpencodingparameters).
+         * The following option would create 3 streams with resolutions if browser supports:
+         * OriginResolution, OriginResolution/2.0 and OriginResolution/4.0.
+         * For current Firefox, the resolutions must be sorted in descending order.
+         * For current Safari, legacy simulcast is used and the parameters like `rid` won't take effect.
+         * Besides `scaleResolutionDownBy`, other `RTCRtpEncodingParameters` can be set
+         * if browser supports.
+         * The actual output will be determined by browsers, the outcome may not be exactly same
+         * as what is set in publishOption, e.g. For a vga video stream, there may be 2 RTP streams
+         * rather than 3.
+         */
+        const publishOption = {video:[
+            {rid: 'q', active: true, scaleResolutionDownBy: 1.0},
+            {rid: 'h', active: true, scaleResolutionDownBy: 2.0},
+            {rid: 'f', active: true, scaleResolutionDownBy: 4.0}
+        ]};
+        /*
+         * Codec priority list.
+         * Here 'vp8' will be used if enabled.
+         */
+        const codecs = ['vp8', 'h264'];
+        localStream = new Owt.Base.LocalStream(
+            stream, new Owt.Base.StreamSourceInfo(
+                'mic', 'camera'));
+        conference.publish(localStream, publishOption, codecs).then(publication => {
+            // ...
+        });
+    });
+~~~~~~
+
+2. Subscribe a simulcast stream
+~~~~~~{.js}
+// Example of subscription.
+conference = new Owt.Conference.ConferenceClient();
+// ...
+conference.join(token).then(resp => {
+    // ...
+    /*
+     * Subscribe simulcast stream with specified `rid`
+     * which can be found in `RemoteStream.settings.video[i].rid`.
+     * If `rid` is set when subscribing, other parameters will be ignored.
+     */
+    const subscribeOption = {
+        audio: true,
+        video: {rid: 'q'}
+    };
+    conference.subscribe(remoteStream, subscribeOption).then((subscription) => {
+        // ...
+    });
+~~~~~~
+
+> **Note:**
+1. The simulcast stream published to conference won't be transcoded.
+2. The `rid` attribute may not be present once a 'streamadded' event triggered. Users should listen on stream's `updated`
+event for new `rid` added.
+3. Current browsers(Chrome/Firefox/Safari) can support VP8 simulcast well while H.264 simulcast has some limitations.