Add support for multi-stream VoIP (#1735)

As per MSC3077.

data/event-schemas/examples/m.call.answer.yaml

@@ -8,6 +8,14 @@
     "answer": {
       "type" : "answer",
       "sdp" : "v=0\r\no=- 6584580628695956864 2 IN IP4 127.0.0.1[...]"
+    },
+    "sdp_stream_metadata": {
+        "271828182845": {
+            "purpose": "m.screenshare"
+        },
+        "314159265358": {
+            "purpose": "m.usermedia"
+        }
     }
   }
 }

data/event-schemas/examples/m.call.invite.yaml

@@ -9,6 +9,14 @@
     "offer": {
       "type" : "offer",
       "sdp" : "v=0\r\no=- 6584580628695956864 2 IN IP4 127.0.0.1[...]"
+    },
+    "sdp_stream_metadata": {
+        "271828182845": {
+            "purpose": "m.screenshare"
+        },
+        "314159265358": {
+            "purpose": "m.usermedia"
+        }
     }
   }
 }

data/event-schemas/examples/m.call.negotiate.yaml

@@ -9,6 +9,14 @@
     "description": {
       "type" : "offer",
       "sdp" : "v=0\r\no=- 6584580628695956864 2 IN IP4 127.0.0.1[...]"
+    },
+    "sdp_stream_metadata": {
+        "271828182845": {
+            "purpose": "m.screenshare"
+        },
+        "314159265358": {
+            "purpose": "m.usermedia"
+        }
     }
   }
 }

data/event-schemas/schema/components/sdp_stream_metadata.yaml

@@ -0,0 +1,27 @@
+type: object
+x-addedInMatrixVersion: "1.10"
+description: |-
+  Metadata describing the [streams](/client-server-api/#streams) that will be
+  sent.
+  
+  This is a map of stream ID to metadata about the stream.
+additionalProperties:
+  type: object
+  title: StreamMetadata
+  description: Metadata describing a stream.
+  properties:
+    purpose:
+      type: string
+      enum:
+        - m.usermedia
+        - m.screenshare
+      description: |-
+        The purpose of the stream.
+
+        The possible values are:
+
+        * `m.usermedia`: Stream that contains the webcam and/or microphone
+          tracks.
+        * `m.screenshare`: Stream with the screen-sharing tracks.
+  required:
+    - purpose

data/event-schemas/schema/m.call.answer.yaml

@@ -27,6 +27,9 @@
                         }
                     },
                     "required": ["type", "sdp"]
+                },
+                "sdp_stream_metadata": {
+                    "$ref": "components/sdp_stream_metadata.yaml"
                 }
             },
             "required": ["answer"]

data/event-schemas/schema/m.call.invite.yaml

@@ -35,7 +35,10 @@
                 "invitee": {
                     "type": "string",
                     "description": "The ID of the user being called. If omitted, any user in the room can answer.",
-                    "x-addedInMatrixVersion": "1.7",
+                    "x-addedInMatrixVersion": "1.7"
+                },
+                "sdp_stream_metadata": {
+                    "$ref": "components/sdp_stream_metadata.yaml"
                 }
             },
             "required": ["offer", "lifetime"]

data/event-schemas/schema/m.call.negotiate.yaml

@@ -63,6 +63,8 @@ properties:
         type: integer
         description: The time in milliseconds that the negotiation is valid for.
           Once the negotiation age exceeds this value, clients should discard it.
+      sdp_stream_metadata:
+        $ref: components/sdp_stream_metadata.yaml
     required:
     - description
     - lifetime