optimize the appicon of iOS

ios/OralTrainer/Services/DubbingCompositor.swift

@@ -0,0 +1,62 @@
+import AVFoundation
+import Foundation
+
+enum DubbingCompositorError: LocalizedError {
+    case noAudioTracks
+    case cannotReadDuration
+
+    var errorDescription: String? {
+        switch self {
+        case .noAudioTracks:
+            return "录音没有音频轨道"
+        case .cannotReadDuration:
+            return "无法读取录音时长"
+        }
+    }
+}
+
+enum DubbingCompositor {
+    static func merge(urls: [URL], outputURL: URL) async throws {
+        try await mergeSync(urls: urls, outputURL: outputURL)
+    }
+
+    private static func mergeSync(urls: [URL], outputURL: URL) async throws {
+        try? FileManager.default.removeItem(at: outputURL)
+        let composition = AVMutableComposition()
+        var currentTime = CMTime.zero
+        for url in urls {
+            let source = AVURLAsset(url: url)
+            let tracks = try await source.loadTracks(withMediaType: .audio)
+            guard let track = tracks.first else {
+                throw DubbingCompositorError.noAudioTracks
+            }
+            let duration = try await source.load(.duration)
+            guard duration.seconds.isFinite, duration.seconds > 0 else {
+                throw DubbingCompositorError.cannotReadDuration
+            }
+            let timeRange = CMTimeRange(start: .zero, duration: duration)
+            let compositionTrack = composition.addMutableTrack(
+                withMediaType: .audio,
+                preferredTrackID: kCMPersistentTrackID_Invalid
+            )
+            guard let compositionTrack else {
+                throw DubbingCompositorError.noAudioTracks
+            }
+            try compositionTrack.insertTimeRange(timeRange, of: track, at: currentTime)
+            currentTime = currentTime + duration
+        }
+
+        guard let exporter = AVAssetExportSession(
+            asset: composition,
+            presetName: AVAssetExportPresetAppleM4A
+        ) else {
+            throw DubbingCompositorError.noAudioTracks
+        }
+        exporter.outputURL = outputURL
+        exporter.outputFileType = .m4a
+        await exporter.export()
+        guard exporter.status == .completed else {
+            throw exporter.error ?? DubbingCompositorError.noAudioTracks
+        }
+    }
+}