degradationPreference only for screen share (#117)

Author: hiroshihorie

Sources/LiveKit/Participant/LocalParticipant.swift

@@ -135,12 +135,15 @@ public class LocalParticipant: Participant {
             track.publishOptions = publishOptions
             track.transceiver = transceiver
 
-            // disable degradationPreference
-            let params = transceiver.sender.parameters
-            params.degradationPreference = NSNumber(value: RTCDegradationPreference.disabled.rawValue)
-            // changing params directly doesn't work so we need to update params
-            // and set it back to sender.parameters
-            transceiver.sender.parameters = params
+            // prefer to maintainResolution for screen share
+            if case .screenShareVideo = track.source {
+                self.log("[publish] set degradationPreference to .maintainResolution")
+                let params = transceiver.sender.parameters
+                params.degradationPreference = NSNumber(value: RTCDegradationPreference.maintainResolution.rawValue)
+                // changing params directly doesn't work so we need to update params
+                // and set it back to sender.parameters
+                transceiver.sender.parameters = params
+            }
 
             self.room.engine.publisherShouldNegotiate()