将 PHAsset（视频）同步转换为 AVAsset

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 AssetsLibrary 已被弃用。现在我到了我有一个 PHAsset 对象数组的地步，我需要将它们转换为 AVAsset。我尝试枚举 PHFetchResult 并使用 PHAsset 的本地化描述分配一个新的 AVAsset，但是当我播放它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];
    }];

我假设本地化描述不是视频的绝对 url。

我也偶然发现了 PHImageManager 和 requestAVAssetForVideo，但是，涉及视频的选项参数没有 isSynchrounous 属性，图像选项参数就是这种情况。

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

有同步的方法吗？

谢谢。

Answer 1

不，没有。但是你可以构建一个同步版本：

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: 花费的时间太长，您可能会锁定 UI 甚至被 iOS watchdog.[=14= 终止]

重新设计您的应用以使用异步回调版本可能更安全。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

你可以试试这个技巧，但当你有 3,4 或 5 个相位集要转换为 AVAsset 时它会很方便：

    [[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，当您将 1 个相集转换为 AVAsset.I 时，您可以再次调用此方法知道这可能不是一个有效的代码，但不应该出于小目的而被禁止。

Answer 3

对于Swift 2，您可以使用下面的方法轻松播放PHAsset的视频，

导入文件

import AVKit

来自 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 4

下面是Swift4的实现，依赖信号量同步发出请求

对代码进行注释以解释各个步骤。

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

导入

import AVKit

Swift 5

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

Answer 6

那些来这里异步方法的人。

Swift 版本：

func requestAVAsset(asset: PHAsset)-> AVAsset? {
        guard asset.mediaType == .video else { return nil }
        let phVideoOptions = PHVideoRequestOptions()
        phVideoOptions.version = .original
        let group = DispatchGroup()
        let imageManager = PHImageManager.default()
        var avAsset: AVAsset?
        group.enter()
        imageManager.requestAVAsset(forVideo: asset, options: phVideoOptions) { (asset, _, _) in
            avAsset = asset
            group.leave()
            
        }
        group.wait()
        
        return avAsset
    }

将 PHAsset（视频）同步转换为 AVAsset

Convert PHAsset (video) to AVAsset, synchronously

video

ios

avasset

photosframework

导入文件

来自 PHAsset

导入

Swift 5