ContinuousScreenSplitter.swift

import AVFoundation
import Foundation
import CoreMedia

class ContinuousSegmenter: NSObject, AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureAudioDataOutputSampleBufferDelegate {
  // MARK: – Configuration
  let segmentDuration: CMTime = .init(seconds: 2, preferredTimescale: 600)
  let outputDir: URL

  // MARK: – Capture
  let session = AVCaptureSession()
  let videoOutput = AVCaptureVideoDataOutput()
  let audioOutput = AVCaptureAudioDataOutput()

  // MARK: – Writer state
  var currentWriter: AVAssetWriter?
  var videoInput: AVAssetWriterInput?
  var audioInput: AVAssetWriterInput?
  var segmentStartTime: CMTime = .zero
  var segmentIndex = 0

  init(outputDir: URL) {
    self.outputDir = outputDir
    super.init()
    setupSession()
    // Prepare first writer starting at time zero
    rollWriter(at: .zero)
  }

  private func setupSession() {
    session.beginConfiguration()
    session.sessionPreset = .high

    // Screen input (main display)
    let displayID = CGMainDisplayID()
    guard let screenIn = AVCaptureScreenInput(displayID: displayID) else {
      fatalError("❌ Unable to create screen input")
    }
    screenIn.minFrameDuration = CMTime(value: 1, timescale: 30)
    screenIn.capturesCursor = true
    session.addInput(screenIn)

    // Audio input (system audio via BlackHole as default)
    guard let audioDev = AVCaptureDevice.default(for: .audio),
          let audioIn = try? AVCaptureDeviceInput(device: audioDev),
          session.canAddInput(audioIn) else {
      fatalError("❌ Unable to create audio input")
    }
    session.addInput(audioIn)

    // Data outputs
    let q = DispatchQueue(label: "segmentation.queue")
    videoOutput.setSampleBufferDelegate(self, queue: q)
    audioOutput.setSampleBufferDelegate(self, queue: q)
    guard session.canAddOutput(videoOutput), session.canAddOutput(audioOutput) else {
      fatalError("❌ Unable to add data outputs")
    }
    session.addOutput(videoOutput)
    session.addOutput(audioOutput)
    session.commitConfiguration()
  }

  private func rollWriter(at startTime: CMTime) {
    // Finish previous writer asynchronously
    if let oldWriter = currentWriter {
      oldWriter.finishWriting {
        print("✅ Finished segment \(self.segmentIndex - 1)")
      }
    }

    // Set up new writer
    do {
      let filename = String(format: "segment_%03d.mov", segmentIndex)
      let fileURL = outputDir.appendingPathComponent(filename)
      try FileManager.default.createDirectory(at: outputDir, withIntermediateDirectories: true)

      let writer = try AVAssetWriter(outputURL: fileURL, fileType: .mov)

      // Video Input Configuration
      let vSettings: [String: Any] = [
        AVVideoCodecKey: AVVideoCodecType.h264,
        AVVideoWidthKey: 1280,
        AVVideoHeightKey: 720
      ]
      let vInput = AVAssetWriterInput(mediaType: .video, outputSettings: vSettings)
      vInput.expectsMediaDataInRealTime = true
      writer.add(vInput)

      // Audio Input Configuration
      let aSettings: [String: Any] = [
        AVFormatIDKey: kAudioFormatMPEG4AAC,
        AVNumberOfChannelsKey: 2,
        AVSampleRateKey: 48000,
        AVEncoderBitRateKey: 128000
      ]
      let aInput = AVAssetWriterInput(mediaType: .audio, outputSettings: aSettings)
      aInput.expectsMediaDataInRealTime = true
      writer.add(aInput)

      // Assign new writer & inputs
      currentWriter = writer
      videoInput = vInput
      audioInput = aInput
      segmentStartTime = startTime
      segmentIndex += 1

      // Start writing session
      writer.startWriting()
      writer.startSession(atSourceTime: startTime)
      print("▶️ Started segment \(segmentIndex - 1) at \(startTime.seconds) s")
    } catch {
      fatalError("❌ Could not start writer: \(error)")
    }
  }

  func start() {
    session.startRunning()
  }

  private func handle(_ sample: CMSampleBuffer, mediaType: AVMediaType) {
    guard CMSampleBufferDataIsReady(sample), currentWriter != nil else { return }

    let pts = CMSampleBufferGetPresentationTimeStamp(sample)

    // Check for segment rollover
    if CMTimeSubtract(pts, segmentStartTime) >= segmentDuration {
      rollWriter(at: pts)
    }

    // Append to writer inputs
    if mediaType == .video, let vInput = videoInput, vInput.isReadyForMoreMediaData {
      vInput.append(sample)
    }
    if mediaType == .audio, let aInput = audioInput, aInput.isReadyForMoreMediaData {
      aInput.append(sample)
    }
  }

  // MARK: – Delegates
  func captureOutput(_ output: AVCaptureOutput,
                     didOutput sampleBuffer: CMSampleBuffer,
                     from connection: AVCaptureConnection) {
    if output === videoOutput {
      handle(sampleBuffer, mediaType: .video)
    } else if output === audioOutput {
      handle(sampleBuffer, mediaType: .audio)
    }
  }
}

// === main ===
let cwd = URL(fileURLWithPath: FileManager.default.currentDirectoryPath)
let segmentsDir = cwd.appendingPathComponent("segments")
let segmenter = ContinuousSegmenter(outputDir: segmentsDir)
segmenter.start()
RunLoop.main.run()