ALAssetsLibraryWriteVideoCompletionBlock 返回未定义的值

ALAssetsLibraryWriteVideoCompletionBlock返回未定义的值。如果 assetURL 等于 nil，那么 error 应该不等于 nil，即返回给我一些错误描述。

请参阅苹果文档：here https://developer.apple.com/library/ios/documentation/AssetsLibrary/Reference/ALAssetsLibrary_Class/Reference/Reference.html#//apple_ref/c/tdef/ALAssetsLibraryWriteVideoCompletionBlock.

当我录制小视频时，ALAssetsLibraryWriteVideoCompletionBlock返回一个很好的 assetURL 值，但是当我录制 3 或 4 Gb 的长视频时，assetURL 返回 nil 并且错误返回 nil。录制的视频位于 tmp 文件中，因为我可以在应用程序的临时文件夹中看到该视频。看起来 iOS 框架尝试将此临时文件复制到相册，而 iPhone 没有足够的内存来将此临时文件复制到相册并返回此文件的路径 (assetURL)。

这是iOS框架中的一个错误吗？如果是这样，有办法解决吗？

更新： 我的文件小于 4GB。谢谢

更新源代码：

    -(void)recorder:(AVCamRecorder *)recorder recordingDidFinishToOutputFileURL:(NSURL *)outputFileURL error:(NSError *)error
    {    
    if ([[self recorder] recordsAudio] && ![[self recorder] recordsVideo]) {
    // If the file was created on a device that doesn't support video recording, it can't be saved to the assets 
    // library. Instead, save it in the app's Documents directory, whence it can be copied from the device via
    // iTunes file sharing.
    [self copyFileToDocuments:outputFileURL];

    if ([[UIDevice currentDevice] isMultitaskingSupported]) {
        [[UIApplication sharedApplication] endBackgroundTask:[self backgroundRecordingID]];
    }       

    if ([[self delegate] respondsToSelector:@selector(captureManagerRecordingFinished:)]) {
        [[self delegate] captureManagerRecordingFinished:self];
    }
}
else {  
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    [library writeVideoAtPathToSavedPhotosAlbum:outputFileURL
                                completionBlock:^(NSURL *assetURL, NSError *error) {
                                    if (error) {
                                        if ([[self delegate] respondsToSelector:@selector(captureManager:didFailWithError:)]) {
                                            [[self delegate] captureManager:self didFailWithError:error];
                                        }                                           
                                    }

                                    if ([[UIDevice currentDevice] isMultitaskingSupported]) {
                                        [[UIApplication sharedApplication] endBackgroundTask:[self backgroundRecordingID]];
                                    }

                                    if (assetURL!=nil)
                                    {
                                        if ([[self delegate] respondsToSelector:@selector(captureManagerRecordingFinished:)]) {
                                        [[self delegate] captureManagerRecordingFinished:self];
                                        }
                                    }
                                    else
                                    {
                                        NSLog(@"Video is not saved");
                                        NSString *alertMsg = [NSString stringWithFormat:@"Impossible to copy video to photo album"];
                                        UIAlertView *alert = [[UIAlertView alloc] init];
                                        [alert setTitle:@"info"];
                                        [alert setMessage:alertMsg];
                                        [alert setDelegate:self];
                                        [alert addButtonWithTitle:@"Accept"];
                                        [alert show];
                                    }
                                }];
     }
}

我有几乎同样的问题：只是我尝试保存照片，而不是电影；但 assetURL 仍然为 NULL。这是我的代码：

    - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
[library writeImageToSavedPhotosAlbum:(__bridge CGImageRef)([info objectForKey:UIImagePickerControllerOriginalImage])
                          orientation:ALAssetOrientationUp completionBlock:^(NSURL *assetURL, NSError *error) {
                              if(error == nil) {
                                  _myImageUrl = [NSString stringWithFormat:@"%@",assetURL];
                                  NSLog(@"%@",assetURL);
                              } else NSLog(@"%@",error);
                          }];

[picker dismissViewControllerAnimated:YES completion:nil];
}

所以，我想这个问题与文件的大小无关。