Convert persisted Data to a temporary URL to configure an AVPlayer for video playback.

DataToURL.swift

import AVFoundation

extension Data {
    func convertToURL() -> URL {
        let tempURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("video").appendingPathExtension("mp4")
        do {
            try self.write(to: tempURL, options: [.atomic])
        } catch {
            print() 
        }
        return tempURL
    }
}

let videoData = Data() // video data from persistence (can be Core Data, Documents Directory, Firebase.....)

// AVPlayer(url: url) needs a URL from a local source to playback video 
let url = videoData.convertToURL()

// Now we can create an instance of AVPlayer with the converted URL 
let player = AVPlayer(url: url)

// The file system will periodically remove temporary files as needed but we can be proactive and remove the file before hand 
do {
    try FileManager.default.removeItem(at: url)
} catch {
    print("failed to remove temporary url with error: \(error)")
}