Fix progress when using VAD chunking

Sources/WhisperKit/Core/WhisperKit.swift

@@ -769,9 +769,12 @@ open class WhisperKit {
         }
         try Task.checkCancellation()
 
+        let childProgress = Progress()
+        progress.totalUnitCount += 1
+        progress.addChild(childProgress, withPendingUnitCount: 1)
         let transcribeTask = TranscribeTask(
             currentTimings: currentTimings,
-            progress: progress,
+            progress: childProgress,
             audioEncoder: audioEncoder,
             featureExtractor: featureExtractor,
             segmentSeeker: segmentSeeker,

Tests/WhisperKitTests/TestUtils.swift

@@ -1,4 +1,5 @@
 import CoreML
+import Combine
 import Foundation
 @testable import WhisperKit
 import XCTest
@@ -274,3 +275,11 @@ extension Collection where Element == TranscriptionResult {
         flatMap(\.segments)
     }
 }
+
+extension Publisher {
+    public func withPrevious() -> AnyPublisher<(previous: Output?, current: Output), Failure> {
+        scan((Output?, Output)?.none) { ($0?.1, $1) }
+            .compactMap { $0 }
+            .eraseToAnyPublisher()
+    }
+}

Tests/WhisperKitTests/UnitTests.swift

@@ -1,6 +1,7 @@
 //  For licensing see accompanying LICENSE.md file.
 //  Copyright © 2024 Argmax, Inc. All rights reserved.
 
+import Combine
 import AVFoundation
 import CoreML
 import Hub
@@ -1178,6 +1179,24 @@ final class UnitTests: XCTestCase {
         XCTAssertTrue(chunkedResult.text.normalized.contains("But then came my 90 page senior".normalized), "Expected text not found in \(chunkedResult.text.normalized)")
     }
 
+    func testVADProgress() async throws {
+        let pipe = try await WhisperKit(model: "tiny.en")
+
+        let cancellable: AnyCancellable? = pipe.progress.publisher(for: \.fractionCompleted)
+            .removeDuplicates()
+            .withPrevious()
+            .sink { previous, current in
+                if let previous {
+                    XCTAssertLessThan(previous, current)
+                }
+            }
+        _ = try await pipe.transcribe(
+            audioPath: Bundle.module.path(forResource: "ted_60", ofType: "m4a")!,
+            decodeOptions: .init(chunkingStrategy: .vad)
+        )
+        cancellable?.cancel()
+    }
+
     // MARK: - Word Timestamp Tests
 
     func testDynamicTimeWarpingSimpleMatrix() {