Add file to Swift Playground on Mac

1. Press the “+” icon

2. Tap the paper icon

3. Tap Insert From…

4. Insert a sound file from the Files app

Code Block 
import AVFoundation
import SwiftUI
import PlaygroundSupport
struct SwiftUIAudioPlayerView: View {
		
		/// the audio player that will play your audio file. Can't be a local variable.
		/// Must be a `@State` property because we need to modify it later
		@State var audioPlayer: AVAudioPlayer?
		
		var body: some View {
				Button(action: {
						self.playAudio() /// play audio when tapped
				}) {
						Text("Play Audio!") /// what the button looks like
				}
		}
		
		func playAudio() { /// function to play audio
				
				/// the URL of the audio file.
				/// forResource = name of the file. 
				/// withExtension = extension, usually "mp3"
				if let audioURL = Bundle.main.url(forResource: "slow-spring-board", withExtension: "mp3") {
						do {
								try self.audioPlayer = AVAudioPlayer(contentsOf: audioURL) /// make the audio player
								self.audioPlayer?.numberOfLoops = 0 /// Number of times to loop the audio
								self.audioPlayer?.play() /// start playing
								
						} catch {
								print("Couldn't play audio. Error: \(error)")
						}
						
				} else {
						print("No audio file found")
				}
		}
}
let swiftuiAudioPlayerView = SwiftUIAudioPlayerView()
PlaygroundPage.current.setLiveView(swiftuiAudioPlayerView)

Code Block 
import AVFoundation
import SwiftUI
import PlaygroundSupport
class UIKitAudioPlayerView: UIView {
		
		/// the audio player that will play your audio file. Can't be a local variable.
		var audioPlayer: AVAudioPlayer?
		
		/// so we only make and connect the button once
		var hasLoadedView = false
		var audioButton = UIButton()
		
		/// the view is guarenteed to be loaded at `layoutSubviews()` 
		override func layoutSubviews() {
				super.layoutSubviews()
				
				if !hasLoadedView {
						hasLoadedView = true
						
						audioButton.setTitle("Play Audio!", for: .normal)
						audioButton.setTitleColor(UIColor.blue, for: .normal)
						backgroundColor = .white
						
						addSubview(audioButton) /// add the button to the view
						audioButton.addTarget(self, action: #selector(playAudio), for: .touchUpInside)
				}
				
				/// positioning (center-align the button)
				let middleXOfView = bounds.width / 2
				let middleYOfView = bounds.height / 2
				let buttonFrame = CGRect(x: middleXOfView - 60, y: middleYOfView - 20, width: 120, height: 40)
				audioButton.frame = buttonFrame
		}
		
		@objc func playAudio() { /// function to play audio
				
				/// the URL of the audio file.
				/// forResource = name of the file. 
				/// withExtension = extension, usually "mp3"
				if let audioURL = Bundle.main.url(forResource: "slow-spring-board", withExtension: "mp3") {
						do {
								try self.audioPlayer = AVAudioPlayer(contentsOf: audioURL) /// make the audio player
								self.audioPlayer?.numberOfLoops = 0 /// Number of times to loop the audio
								self.audioPlayer?.play() /// start playing
								
						} catch {
								print("Couldn't play audio. Error: \(error)")
						}
						
				} else {
						print("No audio file found")
				}
		}
}
let uikitAudioPlayerView = UIKitAudioPlayerView()
PlaygroundPage.current.setLiveView(uikitAudioPlayerView)

The trick here is to use Bundle.main.url(forResource:withExtension:). You MUST do this. If you try adding a file literal via the “+” button (by tapping an already-imported file), it won’t work.