Handles cross-fading between two individual AVPlayers, creates a smooth, undulating loop between two AVPlayerItem's.

AVPlayerCrossFade.swift

import UIKit
import AVFoundation

class ViewController: UIViewController {
    
    // Duplicate players to handle optional cross-fading.
    let playerQueue = [AVPlayer(), AVPlayer()]
    
    var timeObserverToken: Any?

    // Duration for overlapping cross-fade
    var crossFadeDuration: Double = 5.0
    
    /* Returns current AVPlayer */
    var currentPlayer: AVPlayer {
        return self.playingCopy ? self.playerQueue.last! : self.playerQueue.first!
    }
    
    // Init optional cross-fading
    var playingCopy: Bool = false
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        guard let url = URL(string: "https://storage.googleapis.com/slow-69a4e.appspot.com/audio%2F10%20sec_Ocean%2010ms%20fade.mp3?GoogleAccessId=slow-69a4e%40appspot.gserviceaccount.com&Expires=1735689600&Signature=GoDFIQ96SLBtxlQFEz5B5RfUlxrD5SuIy0ZUAC7FITburO5skPskUDj7nDWhkH%2Fn7%2FmuVaKnX9VaLTRQ5BLAxaSLpY5NuGecoPq%2BScdOLrW%2FlCGx0AATsV9fe5rxTRTZzLtv6vj9fLnQEvleZGqYdqBhBw94uDI51N0w2OLCCv8nGBgixrlfNgkSTLJkT541Nc%2FpxzPXyozhjMTFshdTeMEvpLvkzCM9BuSx7ZFBon0HBJ3UlQFz%2FicYUqz5CeTF%2F6n%2BuOX2ujnRk0nbOdVOv%2BIhPeEJispw6Rxz9ludyckMSEdDaBv0DF3Zen6uxnyHL6i5p%2FAZPW33sMnuvA%2FVyQ%3D%3D") else {
            return
        }
        
        // Setup and start main player
        self.currentPlayer.replaceCurrentItem(with: AVPlayerItem(url: url))
        
        // Setup copy
        if let currentItem = self.currentPlayer.currentItem {
            let copy = AVPlayerItem(asset: currentItem.asset)
            self.playerQueue.last?.replaceCurrentItem(with: copy)
        }
        
        // Add volume ramps
        self.addVolumeRamps(with: self.crossFadeDuration)
        
        // Add time observer
        self.addPeriodicTimeObserver(for: self.currentPlayer)
        
        // Start playback
        self.currentPlayer.play()
    }
    
    /// Add volume ramps for all players in queue.
    fileprivate func addVolumeRamps(with duration: Double) {
        for player in self.playerQueue {
            player.currentItem?.addFadeInOut(duration: duration)
        }
    }
    
    /// Add periodic time observer for current player.
    fileprivate func addPeriodicTimeObserver(for player: AVPlayer) {
        self.timeObserverToken = self.currentPlayer.addPeriodicTimeObserver(forInterval: CMTimeMakeWithSeconds(1, preferredTimescale: CMTimeScale(NSEC_PER_SEC)), queue: .main) { [weak self] (currentTime) in
            if let currentItem = self?.currentPlayer.currentItem, currentItem.status == .readyToPlay, let crossFadeDuration = self?.crossFadeDuration {
                let totalDuration = currentItem.asset.duration

                /**
                    Logic for Looping
                 */

                // Start cross-fade logic towards end of playback
                if (CMTimeCompare(currentTime, totalDuration - CMTimeMakeWithSeconds(crossFadeDuration, preferredTimescale: CMTimeScale(NSEC_PER_SEC))) > 0) {
                    
                    // Handle crossfade
                    self?.handleCrossFade()
                }
            }
        }
    }
    
    /// Cycles between players in Queue
    fileprivate func handleCrossFade() {
        
        // Remove current player observer (if any)
        self.removePeriodicTimeObserver(for: self.currentPlayer)
        
        // Invert current player
        self.playingCopy = !self.playingCopy
        
        // Start observing inverted player
        self.addPeriodicTimeObserver(for: self.currentPlayer)

        // Play
        self.currentPlayer.seek(to: .zero)
        self.currentPlayer.play()
    }
    
    /// Remove periodic time observer
    fileprivate func removePeriodicTimeObserver(for player: AVPlayer) {
        if let timeObserverToken = timeObserverToken {
            player.removeTimeObserver(timeObserverToken)
            self.timeObserverToken = nil
        }
    }
}