Add audio only calls support

lib/models/call_member.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_webrtc/media_stream.dart';
 
 /// Single call member information
 ///
@@ -9,10 +10,14 @@ enum MemberStatus { JOINED, READY }
 class CallMember {
   final int userID;
   MemberStatus status;
+  MediaStream stream;
 
   CallMember({
     @required this.userID,
     this.status = MemberStatus.JOINED,
   })  : assert(userID != null),
         assert(status != null);
+
+  bool get hasVideoStream =>
+      stream != null && stream.getVideoTracks().length > 0;
 }

lib/ui/screens/call_screen.dart

@@ -324,7 +324,12 @@ class _CallScreenState extends SafeState<CallScreen> {
       // Register callbacks
       peerConnection.onIceCandidate =
           (c) => CallsHelper.sendIceCandidate(convID, memberID, c);
-      peerConnection.onAddStream = (s) => _renderers[memberID].srcObject = s;
+      peerConnection.onAddStream = (s) {
+        setState(() {
+          _membersList.getUser(memberID).stream = s;
+          _renderers[memberID].srcObject = s;
+        });
+      };
 
       // Request an offer to establish a peer connection
       await CallsHelper.requestOffer(convID, memberID);
@@ -373,7 +378,8 @@ class _CallScreenState extends SafeState<CallScreen> {
 
   /// Call this when a user has interrupted streaming
   Future<void> _removeRemotePeerConnection(int memberID) async {
-    _membersList.getUser(memberID).status = MemberStatus.JOINED;
+    final member = _membersList.getUser(memberID);
+    member.status = MemberStatus.JOINED;
     setState(() {});
 
     if (_peersConnections.containsKey(memberID)) {
@@ -385,6 +391,11 @@ class _CallScreenState extends SafeState<CallScreen> {
       await _renderers[memberID].dispose();
       _renderers.remove(memberID);
     }
+
+    if (member.stream != null) {
+      member.stream.dispose();
+      member.stream = null;
+    }
   }
 
   /// Call this when a member has completely left the call
@@ -491,7 +502,8 @@ class _CallScreenState extends SafeState<CallScreen> {
           // Remove peers videos
           Column(
             children: _membersList.readyPeers
-                .where((f) => _renderers.containsKey(f.userID))
+                .where(
+                    (f) => f.hasVideoStream && _renderers.containsKey(f.userID))
                 .map((f) => _buildMemberVideo(f.userID))
                 .toList(),
           ),
@@ -528,6 +540,7 @@ class _CallScreenState extends SafeState<CallScreen> {
         children: <Widget>[
           // Show / hide user video button
           _FooterButton(
+            visible: _canMakeVideoCall,
             icon: Icon(_isLocalStreamVisible
                 ? Icons.visibility
                 : Icons.visibility_off),
@@ -549,6 +562,7 @@ class _CallScreenState extends SafeState<CallScreen> {
 
           // Toggle video button
           _FooterButton(
+            visible: _canMakeVideoCall,
             icon: Icon(isStreamingVideo && !isVideoMuted
                 ? Icons.videocam
                 : Icons.videocam_off),
@@ -583,17 +597,21 @@ class _CallScreenState extends SafeState<CallScreen> {
 class _FooterButton extends StatelessWidget {
   final Function() onPressed;
   final Widget icon;
+  final bool visible;
 
   const _FooterButton({
     Key key,
     @required this.icon,
     @required this.onPressed,
+    this.visible = true,
   })  : assert(onPressed != null),
         assert(icon != null),
+        assert(visible != null),
         super(key: key);
 
   @override
   Widget build(BuildContext context) {
+    if (!visible) return Container();
     return Expanded(
       child: IconButton(
         icon: icon,