IOS: Subscription update with replacing stream

talk/owt/sdk/conference/conferencesubscription.cc

@@ -127,7 +127,17 @@ void ConferenceSubscription::ApplyOptions(
       });
     }
   } else {
-    that->UpdateSubscription(id_, stream_id_, options, on_success, on_failure);
+    std::string update_stream_id = options.video.streamid;
+    if( update_stream_id.empty() ){
+      that->UpdateSubscription(id_, stream_id_, options, on_success, on_failure);
+    }
+    else{
+      std::function<void()> local_on_success = [this, &update_stream_id, on_success]() {
+         stream_id_.assign(update_stream_id);
+         on_success();
+      };
+      that->UpdateSubscription(id_, update_stream_id, options, local_on_success, on_failure);
+    }
   }
 }
 

talk/owt/sdk/conference/objc/OWTConferenceSubscription.mm

@@ -220,6 +220,8 @@ @implementation OWTConferenceVideoSubscriptionUpdateConstraints
   constrains->frameRate = _frameRate;
   constrains->bitrateMultiplier = _bitrateMultiplier;
   constrains->keyFrameInterval = _keyFrameInterval;
+  if(_streamid != nil)
+    constrains->streamid = std::string([_streamid UTF8String]);
   return constrains;
 }
 @end

talk/owt/sdk/include/cpp/owt/conference/subscribeoptions.h

@@ -56,6 +56,7 @@ struct VideoSubscriptionUpdateConstraints {
   double frameRate;
   double bitrateMultiplier;
   unsigned long keyFrameInterval;
+  std::string streamid;
 };
 /// Subscription update option used by subscription's ApplyOptions API.
 struct SubscriptionUpdateOptions {

talk/owt/sdk/include/objc/OWT/OWTConferenceSubscription.h

@@ -75,6 +75,7 @@ RTC_EXPORT
 @property(nonatomic, assign) double frameRate;
 @property(nonatomic, assign) double bitrateMultiplier;
 @property(nonatomic, assign) NSUInteger keyFrameInterval;
+@property(nonatomic, strong) NSString *streamid;
 @end
 RTC_EXPORT
 @interface OWTConferenceSubscriptionUpdateOptions : NSObject