要解决AVPlayer无法播放3gp视频格式的问题，可以使用AVPlayerItem来处理该视频格式。下面是一个示例代码：

import AVKit

func play3GPVideo(url: URL) {
    let player = AVPlayer(url: url)
    let playerViewController = AVPlayerViewController()
    playerViewController.player = player

    // 监听AVPlayerItem的状态
    player.currentItem?.addObserver(self, forKeyPath: "status", options: [.new, .initial], context: nil)

    // 播放视频
    present(playerViewController, animated: true) {
        player.play()
    }
}

// 监听AVPlayerItem的状态变化
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    guard let playerItem = object as? AVPlayerItem else { return }
    if keyPath == "status" {
        if playerItem.status == .failed {
            print("无法播放该视频格式")
        }
    }
}

使用上述代码，你可以通过调用play3GPVideo(url:)函数来播放3gp视频。如果视频无法播放，将会通过观察AVPlayerItem的状态来捕获错误信息并打印出来。

你需要将要播放的3gp视频的URL传递给play3GPVideo(url:)函数，例如：

let videoURL = URL(string: "https://example.com/video.3gp")!
play3GPVideo(url: videoURL)

请确保替换https://example.com/video.3gp为你要播放的3gp视频的实际URL。