在iOS开发中，如果您想实现自定义画中画（PiP）功能，就需要用到AVPictureInPictureController这个类了，配合AVPlayerLayer、AVPlayer实现视频播放及画中画（PiP）

实现代码

• 配置Audio Playback Behavior，需要设置App 的AVAudioSession的Category为playback模式

   do {
        try AVAudioSession.sharedInstance().setCategory(.playback, mode: .moviePlayback, options: [])
        try AVAudioSession.sharedInstance().setActive(true)
    } catch {
        print("无法设置音频会话类别: \(error)")
    }

• 功能实现

import UIKit
import AVKit
class WSPlayerViewController: UIViewController, AVPictureInPictureControllerDelegate {

    var playerLayer: AVPlayerLayer?
    var pipVC: AVPictureInPictureController?
    var player: AVPlayer?

    init(player:AVPlayer) {
        self.player = player
        
        // 初始化播放图层
        self.playerLayer = AVPlayerLayer(player: player)
        self.playerLayer!.frame = .zero
        self.playerLayer!.videoGravity = .resizeAspect
        self.view.layer.addSublayer(playerLayer!)
        
        // 判断是否支持画中画功能
        if AVPictureInPictureController.isPictureInPictureSupported() {
            let _pipVC = AVPictureInPictureController(playerLayer: self.playerLayer!)
            _pipVC?.delegate = self
            
            if #available(iOS 14.2, *) {
                _pipVC?.canStartPictureInPictureAutomaticallyFromInline = true
            } 
            
            if #available(iOS 14.0, *) {
                _pipVC?.requiresLinearPlayback = true
            }
            //去除播放相关按钮，需要时可选
            //_pipVC?.setValue(1, forKey: "controlsStyle")
            //在 iOS 16 及以上版本支持点击画中画直接回到 App，需要时可选
            //_pipVC?.setValue(2, forKey: "controlsStyle")
        
            self.pipVC = _pipVC
        } else {
            print("当前设备不支持PiP")
        }
  }
  func startPictureInPicture() {
      if self.pipVC?.isPictureInPictureActive == false && self.pipVC?.isPictureInPicturePossible == true {
        self.pipVC?.startPictureInPicture()
      }
  }

  func stopPictureInPicture() {        
      if self.pipVC?.isPictureInPictureActive == true {
          self.pipVC?.stopPictureInPicture()
      }
  }

}

• AVPictureInPictureControllerDelegate代理方法

// 即将开启画中画
func pictureInPictureControllerWillStartPictureInPicture(_ pictureInPictureController: AVPictureInPictureController) {
    print("PIP：即将开启画中画")
}

// 已经开启画中画
func pictureInPictureControllerDidStartPictureInPicture(_ pictureInPictureController: AVPictureInPictureController) {
    print("PIP：已经开启画中画")
}

// 开启画中画失败
func pictureInPictureController(_ pictureInPictureController: AVPictureInPictureController, failedToStartPictureInPictureWithError error: Error) {
    print("PIP：开启画中画失败：\(error)")
}

// 即将关闭画中画
func pictureInPictureControllerWillStopPictureInPicture(_ pictureInPictureController: AVPictureInPictureController) {
    print("PIP：即将关闭画中画")
}

// 已经关闭画中画
func pictureInPictureControllerDidStopPictureInPicture(_ pictureInPictureController: AVPictureInPictureController) {
    print("PIP：已经关闭画中画")
}

// 关闭画中画且恢复播放界面"
func pictureInPictureController(_ pictureInPictureController: AVPictureInPictureController, restoreUserInterfaceForPictureInPictureStopWithCompletionHandler completionHandler: @escaping (Bool) -> Void) {
    print("PIP：关闭画中画且恢复播放界面")
    completionHandler(true)
}

扩展功能

• 添加自定义View
  在创建AVPictureInPictureController之后，系统会创建一个PGHostedWindow，windowLevel 为 -10000000。所以可以通过UIApplication获取到这个window，将自定义的UIView添加到这个 window即可。

   func pictureInPictureControllerWillStartPictureInPicture(_ pictureInPictureController: AVPictureInPictureController) {
        print("PIP：即将开启画中画")
        if let window = UIApplication.shared.windows.first {
            let _customView = UIView()
            let _button = UIButton(type: .custom)
            _button.setTitle("按钮", for: .normal)
            _button.setTitleColor(.white, for: .normal)
            _button.addTarget(self, action: #selector(test), for: .touchUpInside)
            _customView.addSubview(_button)
            _button.snp.makeConstraints { make in
                make.width.equalTo(80)
                make.height.equalTo(40)
                make.center.equalToSuperview()
            }
            window.addSubview(_customView)
            // use autoLayout
            _customView.snp.makeConstraints { (make) -> Void in
                make.edges.equalToSuperview()
            }
        }
    }
  

或

• 设置contentSource，iOS15以上
  将自定义 View 的 layerClass 改写成 AVSampleBufferDisplayerLayer

@implementation PIPCustomView

+ (Class)layerClass {
    return [AVSampleBufferDisplayLayer class];
}

@end

再通过initWithSampleBufferDisplayLayer创建AVPictureInPictureControllerContentSource

let _customView = PIPCustomView()
let _layer = AVSampleBufferDisplayLayer(layer: _customView.layer)
let _source = AVPictureInPictureControllerContentSource(sampleBufferDisplayLayer: _layer, playbackDelegate: _customView)
let _pipVC = AVPictureInPictureController(contentSource: _source)

注意：在自定义的 UIView 添加一个 UIButton，iOS 14、15 可正常执行点击回调方法，iOS 16 及以上则没有任何反应

• 设置PiP播放窗样式

可以通过pipVC.setValue(1, forKey: "controlsStyle")设置
0 = automatic: 系统会根据上下文自动选择适当的控制样式；
1 = minimal: 显示最少的控件，仅包含关闭和恢复全屏按钮；
2 = default: 使用系统的默认控件显示方式；

• 启动画中画的方式
  1. APP在前台直接调用startPictureInPicture即可启动
  2. App 切换到后台时自动开启，将canStartPictureInPictureAutomaticallyFromInline设置为 true 后，可在App切换到后台时自动开启。但需要注意的是该属性只在iOS14.2及以上可用，并且视频必须是在播放中的。

Adopting Picture in Picture in a Custom Player