fix: Make recorder less error-prone (#189)

* Abort recording if failed to start or empty frames

* Activate Audio Session on `cameraQueue`

* Double-check stop recording in callback

* Only call callback once

* Format

* Add description to `.aborted` error

* Update RecordingSession.swift

* Update AVAudioSession+updateCategory.swift

* Rename serial dispatch queues

Author: mrousavy

ios/CameraError.swift

@@ -188,6 +188,7 @@ enum CaptureError {
   case invalidPhotoCodec
   case videoNotEnabled
   case photoNotEnabled
+  case aborted
   case unknown(message: String? = nil)
 
   var code: String {
@@ -210,6 +211,8 @@ enum CaptureError {
       return "video-not-enabled"
     case .photoNotEnabled:
       return "photo-not-enabled"
+    case .aborted:
+      return "aborted"
     case .unknown:
       return "unknown"
     }
@@ -235,6 +238,8 @@ enum CaptureError {
       return "Video capture is disabled! Pass `video={true}` to enable video recordings."
     case .photoNotEnabled:
       return "Photo capture is disabled! Pass `photo={true}` to enable photo capture."
+    case .aborted:
+      return "The capture has been stopped before any input data arrived."
     case let .unknown(message: message):
       return message ?? "An unknown error occured while capturing a video/photo."
     }

ios/CameraQueues.swift

@@ -10,23 +10,26 @@ import Foundation
 
 @objc
 public class CameraQueues: NSObject {
+  
   /// The serial execution queue for the camera preview layer (input stream) as well as output processing of photos.
-  @objc public static let cameraQueue = DispatchQueue(label: "com.mrousavy.vision.camera-queue",
+  @objc public static let cameraQueue = DispatchQueue(label: "mrousavy/VisionCamera.main",
                                                       qos: .userInteractive,
                                                       attributes: [],
                                                       autoreleaseFrequency: .inherit,
                                                       target: nil)
+  
   /// The serial execution queue for output processing of videos as well as frame processors.
-  @objc public static let videoQueue = DispatchQueue(label: "com.mrousavy.vision.video-queue",
+  @objc public static let videoQueue = DispatchQueue(label: "mrousavy/VisionCamera.video",
                                                      qos: .userInteractive,
                                                      attributes: [],
                                                      autoreleaseFrequency: .inherit,
                                                      target: nil)
 
   /// The serial execution queue for output processing of audio buffers.
-  @objc public static let audioQueue = DispatchQueue(label: "com.mrousavy.vision.audio-queue",
+  @objc public static let audioQueue = DispatchQueue(label: "mrousavy/VisionCamera.audio",
                                                      qos: .userInteractive,
                                                      attributes: [],
                                                      autoreleaseFrequency: .inherit,
                                                      target: nil)
+  
 }

ios/CameraView+RecordVideo.swift

@@ -71,9 +71,16 @@ extension CameraView: AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureAud
             }
           }
         }
+
+        self.isRecording = false
         ReactLogger.log(level: .info, message: "RecordingSession finished with status \(status.descriptor).")
+
         if let error = error as NSError? {
-          callback.reject(error: .capture(.unknown(message: "An unknown recording error occured! \(error.description)")), cause: error)
+          if error.domain == "capture/aborted" {
+            callback.reject(error: .capture(.aborted), cause: error)
+          } else {
+            callback.reject(error: .capture(.unknown(message: "An unknown recording error occured! \(error.description)")), cause: error)
+          }
         } else {
           if status == .completed {
             callback.resolve([
@@ -106,28 +113,23 @@ extension CameraView: AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureAud
 
       // Init Audio (optional, async)
       if enableAudio {
-        self.audioQueue.async {
-          // Activate Audio Session (blocking)
-          self.activateAudioSession()
-
-          guard let recordingSession = self.recordingSession else {
-            // recording has already been cancelled
-            return
-          }
-          if let audioOutput = self.audioOutput,
-             let audioSettings = audioOutput.recommendedAudioSettingsForAssetWriter(writingTo: fileType) as? [String: Any] {
-            recordingSession.initializeAudioWriter(withSettings: audioSettings)
-          }
+        // Activate Audio Session (blocking)
+        self.activateAudioSession()
 
-          // Finally start recording, with or without audio.
-          recordingSession.start()
-          self.isRecording = true
+        if let audioOutput = self.audioOutput,
+           let audioSettings = audioOutput.recommendedAudioSettingsForAssetWriter(writingTo: fileType) as? [String: Any] {
+          self.recordingSession!.initializeAudioWriter(withSettings: audioSettings)
         }
-      } else {
-        // start recording session without audio.
-        self.recordingSession!.start()
-        self.isRecording = true
       }
+
+      // start recording session with or without audio.
+      do {
+        try self.recordingSession!.start()
+      } catch {
+        callback.reject(error: .capture(.createRecorderError(message: "RecordingSession failed to start writing.")))
+        return
+      }
+      self.isRecording = true
     }
   }
 

ios/Extensions/AVAudioSession+updateCategory.swift

@@ -11,7 +11,7 @@ import Foundation
 
 extension AVAudioSession {
   /**
-   Calls [setCategory] if the given category or options are not equal to the currently set category and options and reactivates the session.
+   Calls [setCategory] if the given category or options are not equal to the currently set category and options.
    */
   func updateCategory(_ category: AVAudioSession.Category, options: AVAudioSession.CategoryOptions = []) throws {
     if self.category != category || categoryOptions.rawValue != options.rawValue {

ios/React Utils/Callback.swift

@@ -12,27 +12,38 @@ import Foundation
  Represents a callback to JavaScript. Syntax is the same as with Promise.
  */
 class Callback {
+  private var hasCalled = false
+  private let callback: RCTResponseSenderBlock
+
   init(_ callback: @escaping RCTResponseSenderBlock) {
     self.callback = callback
   }
 
   func reject(error: CameraError, cause: NSError?) {
+    guard !hasCalled else { return }
+
     callback([NSNull(), makeReactError(error, cause: cause)])
+    hasCalled = true
   }
 
   func reject(error: CameraError) {
+    guard !hasCalled else { return }
+
     reject(error: error, cause: nil)
+    hasCalled = true
   }
 
-  func resolve(_ value: Any?) {
+  func resolve(_ value: Any) {
+    guard !hasCalled else { return }
+
     callback([value, NSNull()])
+    hasCalled = true
   }
 
   func resolve() {
-    resolve(nil)
-  }
-
-  // MARK: Private
+    guard !hasCalled else { return }
 
-  private let callback: RCTResponseSenderBlock
+    resolve(NSNull())
+    hasCalled = true
+  }
 }

ios/RecordingSession.swift

@@ -16,6 +16,12 @@ enum BufferType {
   case video
 }
 
+// MARK: - RecordingSessionError
+
+enum RecordingSessionError: Error {
+  case failedToStartSession
+}
+
 // MARK: - RecordingSession
 
 class RecordingSession {
@@ -59,6 +65,9 @@ class RecordingSession {
     }
   }
 
+  /**
+   Initializes an AssetWriter for video frames (CMSampleBuffers).
+   */
   func initializeVideoWriter(withSettings settings: [String: Any], isVideoMirrored: Bool) {
     guard !settings.isEmpty else {
       ReactLogger.log(level: .error, message: "Tried to initialize Video Writer with empty settings!", alsoLogToJS: true)
@@ -83,6 +92,9 @@ class RecordingSession {
     ReactLogger.log(level: .info, message: "Initialized Video AssetWriter.")
   }
 
+  /**
+   Initializes an AssetWriter for audio frames (CMSampleBuffers).
+   */
   func initializeAudioWriter(withSettings settings: [String: Any]) {
     guard !settings.isEmpty else {
       ReactLogger.log(level: .error, message: "Tried to initialize Audio Writer with empty settings!", alsoLogToJS: true)
@@ -99,15 +111,34 @@ class RecordingSession {
     ReactLogger.log(level: .info, message: "Initialized Audio AssetWriter.")
   }
 
-  func start() {
-    assetWriter.startWriting()
+  /**
+   Start the Asset Writer(s). If the AssetWriter failed to start, an error will be thrown.
+   */
+  func start() throws {
+    ReactLogger.log(level: .info, message: "Starting Asset Writer(s)...")
+
+    let success = assetWriter.startWriting()
+    if !success {
+      ReactLogger.log(level: .error, message: "Failed to start Asset Writer(s)!")
+      throw RecordingSessionError.failedToStartSession
+    }
+
     initialTimestamp = CMTime(seconds: CACurrentMediaTime(), preferredTimescale: 1_000_000_000)
     assetWriter.startSession(atSourceTime: initialTimestamp!)
     ReactLogger.log(level: .info, message: "Started RecordingSession at \(initialTimestamp!.seconds) seconds.")
   }
 
+  /**
+   Appends a new CMSampleBuffer to the Asset Writer. Use bufferType to specify if this is a video or audio frame.
+   The timestamp parameter represents the presentation timestamp of the buffer, which should be synchronized across video and audio frames.
+   */
   func appendBuffer(_ buffer: CMSampleBuffer, type bufferType: BufferType, timestamp: CMTime) {
+    guard assetWriter.status == .writing else {
+      ReactLogger.log(level: .error, message: "Frame arrived, but AssetWriter status is \(assetWriter.status.descriptor)!")
+      return
+    }
     if !CMSampleBufferDataIsReady(buffer) {
+      ReactLogger.log(level: .error, message: "Frame arrived, but sample buffer is not ready!")
       return
     }
     guard let initialTimestamp = initialTimestamp else {
@@ -138,7 +169,7 @@ class RecordingSession {
       bufferAdaptor.append(imageBuffer, withPresentationTime: timestamp)
       if !hasWrittenFirstVideoFrame {
         hasWrittenFirstVideoFrame = true
-        ReactLogger.log(level: .warning, message: "VideoWriter: First frame arrived \((timestamp - initialTimestamp).seconds) seconds late.")
+        ReactLogger.log(level: .warning, message: "VideoWriter: First frame arrived \((initialTimestamp - timestamp).seconds) seconds late.")
       }
     case .audio:
       guard let audioWriter = audioWriter else {
@@ -156,16 +187,25 @@ class RecordingSession {
     }
 
     if assetWriter.status == .failed {
-      // TODO: Should I call the completion handler or is this instance still valid?
       ReactLogger.log(level: .error,
                       message: "AssetWriter failed to write buffer! Error: \(assetWriter.error?.localizedDescription ?? "none")",
                       alsoLogToJS: true)
+      finish()
     }
   }
 
+  /**
+   Marks the AssetWriters as finished and stops writing frames. The callback will be invoked either with an error or the status "success".
+   */
   func finish() {
     ReactLogger.log(level: .info, message: "Finishing Recording with AssetWriter status \"\(assetWriter.status.descriptor)\"...")
-    if assetWriter.status == .writing {
+
+    if !hasWrittenFirstVideoFrame {
+      let error = NSError(domain: "capture/aborted",
+                          code: 1,
+                          userInfo: [NSLocalizedDescriptionKey: "Stopped Recording Session too early, no frames have been recorded!"])
+      completionHandler(.failed, error)
+    } else if assetWriter.status == .writing {
       bufferAdaptor?.assetWriterInput.markAsFinished()
       audioWriter?.markAsFinished()
       assetWriter.finishWriting {

src/CameraError.ts

@@ -39,6 +39,7 @@ export type CaptureError =
   | 'capture/capture-type-not-supported'
   | 'capture/video-not-enabled'
   | 'capture/photo-not-enabled'
+  | 'capture/aborted'
   | 'capture/unknown';
 export type SystemError = 'system/no-camera-manager';
 export type UnknownError = 'unknown/unknown';