assetのビデオをアプリ内のディレクトリにコピーする方法

asset-library:// にあるビデオをアプリケーション内のディレクトリ(NSDocumentDirectory)とかにコピーしたいこととかありますよね。この場合、NSFileManagerではダメです。

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library assetForURL:assetURL resultBlock:^(ALAsset *asset) {
        ALAssetRepresentation *rep = [asset defaultRepresentation];
        Byte *buffer = (Byte*)malloc(rep.size);
        NSUInteger buffered = [rep getBytes:buffer fromOffset:0.0 length:rep.size error:nil];
        NSData *data = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];
        [data writeToURL:outputURL atomically:YES];
    } failureBlock:^(NSError *error) {
        NSLog(@"%@", [error description]);
    }];

画像の場合はこんな感じかな？

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library assetForURL:assetURL resultBlock:^(ALAsset *asset) {
        ALAssetRepresentation *rep = [asset defaultRepresentation];
        CGImageRef cgImg = [rep fullResolutionImage];
        UIImage *img = [UIImage imageWithCGImage:cgImg];
        NSData *data = UIImagePNGRepresentation(img);
        [data writeToURL:outputURL atomically:YES];
    } failureBlock:^(NSError *error) {
        NSLog(@"%@", [error description]);
    }];