How to add timestamp watermark while recording video? - ios

Question

I'm making iOS video recording app using AVFoundation. Every frame of a video should have timestamp showing time when the video frame was recorded. I looked internet but could not find any reasonable articles.
Here is my current code around video record.
private var session = AVCaptureSession()
private let videoOutput = AVCaptureVideoDataOutput()
private let audioOutput = AVCaptureAudioDataOutput()
private func setupCaptureSession() {
session.sessionPreset = .vga640x480
guard
let videoDevice = AVCaptureDevice.default(for: .video),
let audioDevice = AVCaptureDevice.default(for: .audio),
let videoInput = try? AVCaptureDeviceInput(device: videoDevice),
let audioInput = try? AVCaptureDeviceInput(device: audioDevice) else {
fatalError()
}
session.beginConfiguration()
session.addInput(videoInput)
session.addInput(audioInput)
session.addOutput(videoOutput)
session.addOutput(audioOutput)
session.commitConfiguration()
DispatchQueue.main.async {
let previewView = PreviewView()
previewView.videoPreviewLayer.session = self.session
previewView.videoPreviewLayer.connection?.videoOrientation = .landscapeRight
previewView.frame = self.view.bounds
previewView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
self.compositeImageView.insertSubview(previewView, at: 0)
self.session.startRunning()
}
}
private func startRecording() {
// AVAssetWriter
assetWriter = try! AVAssetWriter(outputURL: self.exportURL!, fileType: .mov)
// video
let videoInput = AVAssetWriterInput(mediaType: .video, outputSettings: [
AVVideoCodecKey : AVVideoCodecType.h264,
AVVideoWidthKey : 640,
AVVideoHeightKey : 480
])
videoInput.expectsMediaDataInRealTime = true
assetWriter?.add(videoInput)
// audio
let audioInput = AVAssetWriterInput(mediaType: .audio, outputSettings: nil)
audioInput.expectsMediaDataInRealTime = true
assetWriter?.add(audioInput)
assetWriter?.startWriting()
let queue = DispatchQueue.global()
videoOutput.setSampleBufferDelegate(self, queue: queue)
audioOutput.setSampleBufferDelegate(self, queue: queue)
}
private func finishRecording() {
videoOutput.setSampleBufferDelegate(nil, queue: nil)
audioOutput.setSampleBufferDelegate(nil, queue: nil)
startTime = nil
assetWriter?.finishWriting { [weak self] in
guard let self = self else { return }
guard self.assetWriter!.status == .completed else { fatalError("failed recording") }
self.saveToPhotoLibrary { isSaveToPhotoLibrarySucceed in
print("vide saved to photo library")
guard isSaveToPhotoLibrarySucceed else {
print("Save to photo library failed")
return
}
self.saveToRealmFromTempVideo {
self.uploadVideoToServer()
}
}
}
}
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
guard isRecording else { fatalError() }
guard CMSampleBufferDataIsReady(sampleBuffer) else {
print("not ready")
return
}
if startTime == nil {
startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
assetWriter?.startSession(atSourceTime: startTime!)
}
// Append video or audio
let mediaType: AVMediaType = output is AVCaptureVideoDataOutput ? .video : .audio
if mediaType == .video {
appendVideo(from: sampleBuffer)
} else if mediaType == .audio {
appendAudio(from: sampleBuffer)
} else {
fatalError("should not reach here")
}
}