Implement rate control

Sources/LiveKit/Broadcast/IPC/BroadcastUploader.swift

@@ -25,6 +25,8 @@ final class BroadcastUploader: Sendable {
     private let channel: IPCChannel
     private let imageCodec = BroadcastImageCodec()
 
+    @Atomic private var isUploading = false
+
     enum Error: Swift.Error {
         case unsupportedSample
     }
@@ -46,9 +48,13 @@ final class BroadcastUploader: Sendable {
 
     /// Upload a sample from ReplayKit.
     func upload(_ sampleBuffer: CMSampleBuffer, with type: RPSampleBufferType) async throws {
-        switch type {
-        case .video: try await sendImage(sampleBuffer)
-        default: throw Error.unsupportedSample
+        guard type == .video else { throw Error.unsupportedSample }
+        guard !isUploading else { return }
+        try await asyncDefer {
+            isUploading = true
+            try await sendImage(sampleBuffer)
+        } defer: {
+            isUploading = false
         }
     }
 
@@ -88,4 +94,18 @@ private extension VideoRotation {
     }
 }
 
+private func asyncDefer<T>(
+    _ task: () async throws -> T,
+    defer cleanUp: () -> Void
+) async rethrows -> T {
+    do {
+        let result = try await task()
+        cleanUp()
+        return result
+    } catch {
+        cleanUp()
+        throw error
+    }
+}
+
 #endif

Sources/LiveKit/Broadcast/Uploader/Atomic.swift

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2025 LiveKit
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import Foundation
+
+@propertyWrapper
+struct Atomic<Value> {
+    private var value: Value
+    private let lock = NSLock()
+
+    init(wrappedValue value: Value) {
+        self.value = value
+    }
+
+    var wrappedValue: Value {
+        get { load() }
+        set { store(newValue: newValue) }
+    }
+
+    func load() -> Value {
+        lock.lock()
+        defer { lock.unlock() }
+        return value
+    }
+
+    mutating func store(newValue: Value) {
+        lock.lock()
+        defer { lock.unlock() }
+        value = newValue
+    }
+}