WIP - implement ChunkedRecorder

- configure AVAssetWriter for fragmented mp4 output
- implement ChunkedRecorder to received chunk data via AVAssetWriterDelegate

package/ios/Core/ChunkedRecorder.swift

@@ -0,0 +1,70 @@
+//
+//  ChunkedRecorder.swift
+//  VisionCamera
+//
+//  Created by Rafael Bastos on 12/07/2024.
+//  Copyright © 2024 mrousavy. All rights reserved.
+//
+
+import Foundation
+import AVFoundation
+
+
+class ChunkedRecorder: NSObject {
+  
+  let outputURL: URL
+  
+  private var initSegment: Data?
+  private var index: Int = 0
+  
+  init(url: URL) throws {
+    outputURL = url
+    
+    guard FileManager.default.fileExists(atPath: outputURL.path) else {
+      throw CameraError.unknown(message: "output directory does not exist at: \(outputURL.path)", cause: nil)
+    }
+  }
+  
+}
+
+extension ChunkedRecorder: AVAssetWriterDelegate {
+  
+  func assetWriter(_ writer: AVAssetWriter, 
+                   didOutputSegmentData segmentData: Data,
+                   segmentType: AVAssetSegmentType,
+                   segmentReport: AVAssetSegmentReport?) {
+    
+    switch segmentType {
+    case .initialization:
+      saveInitSegment(segmentData)
+    case .separable:
+      saveSegment(segmentData)
+    @unknown default:
+      fatalError("Unknown AVAssetSegmentType!")
+    }
+  }
+  
+  private func saveInitSegment(_ data: Data) {     
+    initSegment = data
+  }
+  
+  private func saveSegment(_ data: Data) {
+    guard let initSegment else {
+      print("missing init segment")
+      return
+    }
+    
+    let file = String(format: "%06d.mp4", index)
+    index += 1
+    let url = outputURL.appendingPathComponent(file)
+    
+    do {
+      let outputData = initSegment + data
+      try outputData.write(to: url)
+      print("writing", data.count, "to", url)
+    } catch {
+      print("Error--->", error)
+    }
+  }
+  
+}

package/ios/Core/RecordingSession.swift

@@ -29,6 +29,7 @@ class RecordingSession {
   private let assetWriter: AVAssetWriter
   private var audioWriter: AVAssetWriterInput?
   private var videoWriter: AVAssetWriterInput?
+  private let recorder: ChunkedRecorder
   private let completionHandler: (RecordingSession, AVAssetWriter.Status, Error?) -> Void
 
   private var startTimestamp: CMTime?
@@ -49,7 +50,8 @@ class RecordingSession {
    Gets the file URL of the recorded video.
    */
   var url: URL {
-    return assetWriter.outputURL
+    // FIXME:
+    return recorder.outputURL
   }
 
   /**
@@ -76,8 +78,24 @@ class RecordingSession {
     completionHandler = completion
 
     do {
-      assetWriter = try AVAssetWriter(outputURL: url, fileType: fileType)
+      recorder = try ChunkedRecorder(url: url.deletingLastPathComponent())
+      assetWriter = AVAssetWriter(contentType: UTType(fileType.rawValue)!)
       assetWriter.shouldOptimizeForNetworkUse = false
+      assetWriter.outputFileTypeProfile = .mpeg4AppleHLS
+      assetWriter.preferredOutputSegmentInterval = CMTime(seconds: 6, preferredTimescale: 1)
+      
+      /*
+        Apple HLS fMP4 does not have an Edit List Box ('elst') in an initialization segment to remove
+        audio priming duration which advanced audio formats like AAC have, since the sample tables
+        are empty.  As a result, if the output PTS of the first non-fully trimmed audio sample buffer is
+        kCMTimeZero, the audio samples’ presentation time in segment files may be pushed forward by the
+        audio priming duration.  This may cause audio and video to be out of sync.  You should add a time
+        offset to all samples to avoid this situation.
+      */
+      let startTimeOffset = CMTime(value: 10, timescale: 1)
+      assetWriter.initialSegmentStartTime = startTimeOffset
+      
+      assetWriter.delegate = recorder
     } catch let error as NSError {
       throw CameraError.capture(.createRecorderError(message: error.description))
     }