Add support for muting in VoIP calls (#1755)

As per MSC3291.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

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

@@ -0,0 +1,16 @@
+{
+  "$ref": "core/room_event.json",
+  "type": "m.call.sdp_stream_metadata_changed",
+  "content": {
+    "version": "1",
+    "call_id": "1414213562373095",
+    "party_id": "1732050807568877",
+    "sdp_stream_metadata": {
+        "2311546231": {
+            "purpose": "m.usermedia",
+            "audio_muted:": true,
+            "video_muted": true
+        }
+    }
+  }
+}

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

@@ -13,8 +13,8 @@ additionalProperties:
     purpose:
       type: string
       enum:
-        - m.usermedia
-        - m.screenshare
+      - m.usermedia
+      - m.screenshare
       description: |-
         The purpose of the stream.
 
@@ -23,5 +23,19 @@ additionalProperties:
         * `m.usermedia`: Stream that contains the webcam and/or microphone
           tracks.
         * `m.screenshare`: Stream with the screen-sharing tracks.
+    audio_muted:
+      type: boolean
+      description: |-
+        Whether the audio track in the stream is muted.
+
+        Defaults to `false` if not present.
+      x-addedInMatrixVersion: "1.11"        
+    video_muted:
+      type: boolean
+      description: |-
+        Whether the video track in the stream is muted.
+
+        Defaults to `false` if not present.
+      x-addedInMatrixVersion: "1.11"        
   required:
-    - purpose
+  - purpose

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

@@ -0,0 +1,21 @@
+type: object
+x-addedInMatrixVersion: "1.11"
+description: |-
+  This event is sent by callers when they wish to update a stream's metadata
+  but no negotiation is required.
+allOf:
+  - $ref: core-event-schema/room_event.yaml
+properties:
+  content:
+    type: object
+    allOf:
+    - $ref: core-event-schema/call_event.yaml
+    properties:
+      sdp_stream_metadata:
+        $ref: components/sdp_stream_metadata.yaml
+    required:
+    - sdp_stream_metadata
+  type:
+    type: string
+    enum:
+    - m.call.sdp_stream_metadata_changed