ios - 使用 PhotoKit (iOS8) 从视频中获取海报帧

Question

我想从视频资源中提取 UIimage，用作海报。根据 PHImageManager 的文档，我应该能够使用 requestImageForAsset:targetSize:contentMode:options:resultHandler:。引用文档:

You can use this method for both photo and video assets—for a video asset, an image request provides a thumbnail image or poster frame.

虽然这不是我的经验。将 requestImageForAsset:targetSize:contentMode:options:resultHandler: 与视频 Assets 一起使用，回调 block 始终为图像返回 nil 和 nil 错误。返回的信息字典看起来如下(我无法理解)

{
PHImageFileSandboxExtensionTokenKey = "31c0997752ae82ee32953503bd6d9a2436c50fac;00000000;00000000;000000000000001a;com.apple.app-sandbox.read;00000001;01000003;0000 0000000756cf;/private/var/mobile/Media/DCIM/100APPLE/IMG_0008.MOV";
PHImageFileURLKey = "文件:///var/mobile/Media/DCIM/100APPLE/IMG_0008.MOV";
PHImageFileUTIKey = "dyn.ah62d4uv4ge804550";
PHImageResultDeliveredImageFormatKey = 9999;
PHImageResultIsDegradedKey = 0;
PHImageResultIsInCloudKey = 0;
PHImageResultIsPlaceholderKey = 0;
PHImageResultRequestIDKey = 26;
PHImageResultWantedImageFormatKey = 9999;
}


这是我在 PHAsset 类别中编写的方法，用于从下面的视频 PHAsset 中提取图像。有没有人能够做到这一点？

@implementation PHAsset (util)

-(PHImageRequestID)fullSizeImage: (void(^)(UIImage *image, NSError *error)) resultHandler {
  PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];

  PHImageContentMode contentMode = PHImageContentModeAspectFill ;

  PHImageManager *imageManager = [PHImageManager defaultManager] ;
  CGSize targetSize = PHImageManagerMaximumSize ;
  return [imageManager requestImageForAsset:self targetSize:targetSize contentMode:contentMode options:nil resultHandler:^(UIImage *result, NSDictionary *info) {
    NSError *error  = (NSError*)[info objectForKey:PHImageErrorKey];
    if (result == nil) {
      NSLog(@"ERROR while fetching fullSizeImage %@, info:\n%@", error, info);
    }

    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
      resultHandler(result, error);
    }];
  }];
}

@end

Answer 1

替换后我让它工作

CGSize targetSize = PHImageManagerMaximumSize ;

与...

CGSize targetSize = CGSizeMake(self.pixelWidth*ratio, self.pixelHeight*ratio) ;

我还没有看到任何相关文档，所以可能是 iOS8.0.x 中的一个错误(在撰写本文时，iOS8.1 beta 可用，但我尚未对其进行测试)