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Set up an external camera source

ViewController
import AVFoundation
import MapboxVision
import UIKit
/**
* "External camera" example demonstrates how to create a custom source of a video stream
* and pass it to `VisionManager`.
* **Important:** To enable most of the features of Vision SDK like world description, AR and Safety, the object
* implementing the `VideoSource` protocol should also provide `CameraParameters`.
* Reading a file is an example of implementing `VideoSource` protocol. Do not feed recorded videos in production
* as the video will not match other realtime data (GPS, motion sensors) causing incorrect values
* for most of the features.
*/
// Example of custom video source is a simple video file reader
class FileVideoSource: ObservableVideoSource {
private let reader: AVAssetReader?
private let queue = DispatchQueue(label: "FileVideoSourceQueue")
private lazy var timer: CADisplayLink = {
let displayLink = CADisplayLink(target: self, selector: #selector(update))
displayLink.preferredFramesPerSecond = 30
return displayLink
}()
init(url: URL) {
let asset = AVAsset(url: url)
reader = try? AVAssetReader(asset: asset)
super.init()
let videoTrack = asset.tracks(withMediaType: .video).first!
let output = AVAssetReaderTrackOutput(
track: videoTrack,
outputSettings: [
String(kCVPixelBufferPixelFormatTypeKey): NSNumber(value: kCVPixelFormatType_32BGRA)
]
)
reader?.add(output)
}
func start() {
queue.async { [unowned self] in
self.reader?.startReading()
self.timer.add(to: .main, forMode: .default)
}
}
func stop() {
queue.async { [unowned self] in
self.stopReading()
}
}
@objc
func update() {
queue.async { [unowned self] in
if let buffer = self.reader?.outputs.first?.copyNextSampleBuffer() {
// notify all abservers about new sample buffer availability
self.notify { observer in
// construct `VideoSample` specifying the format of image contained in a sample buffer
let videoSample = VideoSample(buffer: buffer, format: .BGRA)
observer.videoSource(self, didOutput: videoSample)
// Obtain camera parameters and set them each time they change
// let cameraParameters = CameraParameters(width: width, height: height,
// focalXPixels: focalPixelX, focalYPixels: focalPixelY)
// observer.videoSource(self, didOutput: cameraParameters)
}
} else {
self.stopReading()
}
}
}
private func stopReading() {
timer.invalidate()
reader?.cancelReading()
}
}
class ExternalCameraViewController: UIViewController, VisionManagerDelegate {
private var fileVideoSource: FileVideoSource!
private var visionManager: VisionManager!
private let visionViewController = VisionPresentationViewController()
override func viewDidLoad() {
super.viewDidLoad()
addVisionView()
// create a custom video source and subscribe to receiving new video samples
fileVideoSource = FileVideoSource(url: Bundle.main.url(forResource: "video", withExtension: "mp4")!)
// create VisionManager with a custom video source
visionManager = VisionManager.create(videoSource: fileVideoSource)
visionManager.delegate = self
// configure view to display sample buffers from video source
visionViewController.set(visionManager: visionManager)
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
visionManager.start()
fileVideoSource.start()
}
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
fileVideoSource.stop()
visionManager.stop()
}
private func addVisionView() {
addChild(visionViewController)
view.addSubview(visionViewController.view)
visionViewController.didMove(toParent: self)
}
deinit {
// free up VisionManager's resources
visionManager.destroy()
}
}