Question

我需要使用AVAsset对象，以便使用AVPlayer和AVPlayerLayer播放它。我开始使用Photos框架，因为不推荐使用AssetsLibrary。现在我到了我有一个PHAsset对象数组的点，我需要将它们转换为AVAsset。我尝试通过PHFetchResult枚举并使用PHAsset的本地化描述分配新的AVAsset，但是当我播放时它似乎没有显示任何视频。

    PHAssetCollection *assetColl = [self scaryVideosAlbum];

    PHFetchResult *getVideos = [PHAsset fetchAssetsInAssetCollection:assetColl options:nil];

    [getVideos enumerateObjectsUsingBlock:^(PHAsset *asset, NSUInteger idx, BOOL *stop) {
            NSURL *videoUrl = [NSURL URLWithString:asset.localizedDescription];
            AVAsset *avasset = [AVAsset assetWithURL:videoUrl];
            [tempArr addObject:avasset];
    }];

我认为本地化描述不是视频的绝对网址。

我也偶然发现了PHImageManager和requestAVAssetForVideo，但是当视频归结为视频时，options参数没有isSynchrounous属性，就像image options参数一样。

        PHVideoRequestOptions *option = [PHVideoRequestOptions new];
        [[PHImageManager defaultManager] requestAVAssetForVideo:videoAsset options:option resultHandler:^(AVAsset * _Nullable avasset, AVAudioMix * _Nullable audioMix, NSDictionary * _Nullable info) {

有同步方法吗？

感谢。

Answer 1

不，没有。但是可以构建同步版本：

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];

但是，如果您在主线程上执行此操作并且requestAVAssetForVideo:花费的时间过长，则可能会锁定您的用户界面甚至被iOS watchdog终止。

使用异步回调版本重写您的应用程序可能更安全。像这样：

__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];
    });
}];

Answer 2

对于 Swift 2 ，您可以使用以下方法轻松地使用PHAsset播放视频，

导入文件

import AVKit

从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()
                }
            })
        })
    }

Answer 3

你可以试试这个技巧但是当你想要转换为AVAsset的3,4或5个phasset时它很方便：

    [[PHImageManager defaultManager] requestAVAssetForVideo:assetsArray[0] options:option resultHandler:^(AVAsset * avasset, AVAudioMix * audioMix, NSDictionary * info) {
//do something with this asset
       [[PHImageManager defaultManager] requestAVAssetForVideo:assetsArray[1] options:option resultHandler:^(AVAsset * avasset, AVAudioMix * audioMix, NSDictionary * info) {
//so on...
       }
        }

所以基本上，当你将1个phasset转换为AVAsset时，你可以再次调用这个方法。我知道这可能不是一个有效的代码，但不应该为了很少的目的而禁止它。

Answer 4

以下是Swift 4实现，它依赖于信号量来同步发出请求。

对代码进行了评论，以解释各个步骤。

func requestAVAsset(asset: PHAsset) -> AVAsset? {
    // We only want videos here
    guard asset.mediaType == .video else { return nil }
    // Create your semaphore and allow only one thread to access it
    let semaphore = DispatchSemaphore.init(value: 1)
    let imageManager = PHImageManager()
    var avAsset: AVAsset?
    // Lock the thread with the wait() command
    semaphore.wait()
    // Now go fetch the AVAsset for the given PHAsset
    imageManager.requestAVAsset(forVideo: asset, options: nil) { (asset, _, _) in
        // Save your asset to the earlier place holder
        avAsset = asset
        // We're done, let the semaphore know it can unlock now
        semaphore.signal()
    }

    return avAsset
}

Answer 5

您可以使用此：

let asset = info[UIImagePickerControllerPHAsset] as? PHAsset

PHCachingImageManager().requestAVAsset(forVideo: phAsset, options: nil) { (avAsset, _, _) in
    if let avAsset = avAsset {
        print(avAsset)
    }
}

同步将PHAsset（视频）转换为AVAsset

5 个答案:

导入文件

从PHAsset