Picture in Picture in Swift

1. **Picture-in-Picture (PiP) Mode**: 
    - You can use the `AVPlayerViewController` class which supports PiP mode¹.
    - If you're building a custom video player, you can use `AVPictureInPictureController`².
    - To enable PiP mode automatically from inline, you can use `pictureInPictureController.canStartPictureInPictureAutomaticallyFromInline = true`⁴.
2. **Background Mode**:
    - To allow your app to perform tasks in the background, you need to enable the background capabilities in Xcode⁶.
    - You can use `BGAppRefreshTask` for short-duration tasks that expect quick results, such as downloading a stock quote⁶.
    - For tasks that might be time-consuming, such as downloading a large file or synchronizing data, you can use `BGProcessingTask`⁶.
    - You can also use the `application:performFetchWithCompletionHandler()` function which is invoked by the system every time the app is launched in the background⁹.
Implementing Picture-in-Picture (PiP) mode in your iOS app involves several steps¹²³⁴:

1. **Add Background Mode Capability to Your App**: The first step is to add the Background Mode capability and then turn on the Audio, AirPlay, and Picture in Picture flag in Xcode GUI under the Signing & Capabilities section¹⁴.

2. **Request for Background Mode Playback Access**: The second step is to setup the `AVAudioSession.sharedInstance()` category before the VideoPlayer is instantiated¹. Here's how you can do it:

swift

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    requestPIPBackgroundMode()
    return true
}
private func requestPIPBackgroundMode() {
    let session = AVAudioSession.sharedInstance()
    do {
        try session.setCategory(.playback, mode: .moviePlayback)
    } catch let error {
        print(error.localizedDescription)
    }
}

3. **Implement PiP Functionality**: To implement PiP functionality in your app, you'll leverage the power of AVKit and AVFoundation frameworks¹. AVKit provides a comprehensive set of tools and components specifically designed for media playback, while AVFoundation offers the underlying functionality for working with audiovisual media¹. With both frameworks, you can create an `AVPlayerViewController` instance and associate it with the desired video content that you want to enable PiP for or you can even create your own custom video player with the help of the `AVPlayer` API¹.
Remember, debugging issues with PiP mode can be complex and may require a thorough examination of your code and network setup.