同步将PHAsset（视频）转换为AVAsset [英] Convert PHAsset (video) to AVAsset, synchronously

问题描述

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进行枚举并使用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。

I need to use the AVAsset object, in order to play it using AVPlayer and AVPlayerLayer. I started using the Photos framework since AssetsLibrary is deprecated. Now I got to the point where I have an array of PHAsset objects and I need to convert them to AVAsset. I tried enumerating through the PHFetchResult and allocation a new AVAsset using the PHAsset's localized description, but it does not seem to show any video when I play it.

    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。

I assume the localized description is not the absolute url of the video.

我也偶然发现了PHImageManager和requestAVAssetForVideo，但是，当涉及到视频时，options参数没有isSynchrounous属性，这是image options参数的情况。

I also stumbled upon the PHImageManager and the requestAVAssetForVideo, however, the options parameter when it comes down to video does not have an isSynchrounous property, which is the case with the image options parameter.

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

有同步方式吗？

谢谢。

推荐答案

不，没有。但是可以构建同步版本：

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];

但是如果你在主线程上执行此操作并且 requestAVAssetForVideo：花费太长时间，您可能会锁定您的用户界面甚至被 iOS看门狗。

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.

使用异步回调版本重做你的应用程序可能更安全。这样的事情：

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];
    });
}];

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