Use L1T3 for screen sharing

Author: pblazej

Sources/LiveKit/Support/Utils.swift

@@ -223,9 +223,14 @@ class Utils: Loggable {
         let videoCodec = overrideVideoCodec ?? publishOptions.preferredCodec
 
         if let videoCodec, videoCodec.isSVC {
-            // SVC mode
-            log("Using SVC mode")
-            return [RTC.createRtpEncodingParameters(encoding: encoding, scalabilityMode: .L3T3_KEY)]
+            // VP9/AV1 with screen sharing requires single spatial layer
+            if isScreenShare {
+                log("Using SVC mode with L1T3 for screen sharing")
+                return [RTC.createRtpEncodingParameters(encoding: encoding, scalabilityMode: .L1T3)]
+            } else {
+                log("Using SVC mode")
+                return [RTC.createRtpEncodingParameters(encoding: encoding, scalabilityMode: .L3T3_KEY)]
+            }
         } else if !publishOptions.simulcast {
             // Not-simulcast mode
             log("Simulcast not enabled")

Sources/LiveKit/Types/ScalabilityMode.swift

@@ -21,11 +21,13 @@ public enum ScalabilityMode: Int {
     case L3T3 = 1
     case L3T3_KEY = 2
     case L3T3_KEY_SHIFT = 3
+    case L1T3 = 4
 }
 
 public extension ScalabilityMode {
     static func fromString(_ rawString: String?) -> ScalabilityMode? {
         switch rawString {
+        case "L1T3": .L1T3
         case "L3T3": .L3T3
         case "L3T3_KEY": .L3T3_KEY
         case "L3T3_KEY_SHIFT": .L3T3_KEY_SHIFT
@@ -35,13 +37,19 @@ public extension ScalabilityMode {
 
     var rawStringValue: String {
         switch self {
+        case .L1T3: "L1T3"
         case .L3T3: "L3T3"
         case .L3T3_KEY: "L3T3_KEY"
         case .L3T3_KEY_SHIFT: "L3T3_KEY_SHIFT"
         }
     }
 
-    var spatial: Int { 3 }
+    var spatial: Int {
+        switch self {
+        case .L1T3: 1
+        case .L3T3, .L3T3_KEY, .L3T3_KEY_SHIFT: 3
+        }
+    }
 
     var temporal: Int { 3 }
 }