Convert PHAsset (video) to AVAsset, synchronously

No, there isn't. But you can build a synchronous version:

dispatch_semaphore_t    semaphore = dispatch_semaphore_create(0);

PHVideoRequestOptions *option = [PHVideoRequestOptions new];
__block AVAsset *resultAsset;

[[PHImageManager defaultManager] requestAVAssetForVideo:videoAsset options:option resultHandler:^(AVAsset * avasset, AVAudioMix * audioMix, NSDictionary * info) {
    resultAsset = avasset;
    dispatch_semaphore_signal(semaphore);
}];

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
// yay, we synchronously have the asset
[self doSomethingWithAsset:resultAsset];

However if you do this on the main thread and requestAVAssetForVideo: takes too long, you risk locking up your UI or even being terminated by the iOS watchdog.

It's probably safer to rework your app to work with the asynchronous callback version. Something like this:

__weak __typeof(self) weakSelf = self;

[[PHImageManager defaultManager] requestAVAssetForVideo:videoAsset options:option resultHandler:^(AVAsset * avasset, AVAudioMix * audioMix, NSDictionary * info) {
    dispatch_async(dispatch_get_main_queue(), ^{
        [weakSelf doSomethingWithAsset:avasset];
    });
}];

Import

import AVKit

Swift 5

let phAsset = info[UIImagePickerControllerPHAsset] as? PHAsset
    
PHCachingImageManager().requestAVAsset(forVideo: phAsset, options: nil) { (avAsset, _, _) in
    print(avAsset)
}

For Swift 2, you can easily play the video with PHAsset using this method below,

Import File

import AVKit

From PHAsset

static func playVideo (view:UIViewController, asset:PHAsset) {

        guard (asset.mediaType == PHAssetMediaType.Video)

            else {
                print("Not a valid video media type")
                return
        }

        PHCachingImageManager().requestAVAssetForVideo(asset, options: nil, resultHandler: {(asset: AVAsset?, audioMix: AVAudioMix?, info: [NSObject : AnyObject]?) in

            let asset = asset as! AVURLAsset

            dispatch_async(dispatch_get_main_queue(), {

                let player = AVPlayer(URL: asset.URL)
                let playerViewController = AVPlayerViewController()
                playerViewController.player = player
                view.presentViewController(playerViewController, animated: true) {
                    playerViewController.player!.play()
                }
            })
        })
    }