how to check if a file ( video) is already in ALAssetsLibrary (photo album ) before saving it?

Question

I'm saving a file from a server to ALAssetLibrary so that the user can view it in offline mode

however i don't want the user to download a single file multiple times to avoid creating duplicates in the photo album application.

that's my code :

    ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];

        void (^completionBlock)(NSURL *, NSError *) = ^(NSURL *assetURL, NSError *error)
        {
            if ( error != nil )
            {
                //writeFailed = YES;
                NSLog(@"error = %@", error);
            }

            //[self notifyCompletionTarget];
            NSLog(@" saving is done");
        };

        NSURL *url = [[NSURL alloc] initFileURLWithPath:path];

        [library writeVideoAtPathToSavedPhotosAlbum:url completionBlock:completionBlock ];
    }

Answer 1

I think You Cant . You can use many algorithms to compare the files like SHA-1, MD5,CRC etc . However in the case of ALAsset , the mentioned all will fail.

Because , Whenever you are saving a file to Photo-Library using ALAsset , it will store the location, time,etc .. information's with the file. So the same file contend will be different corresponding to the save process .

The all above algorithms are regarding to the file contend.So they all will fail in the case of ALAsset