Save resource video file to photo library using asset library.

SaveVideoToAsset.m

NSURL* videoURL = [[NSBundle mainBundle] URLForResource:@"demo-clip" withExtension:@"mp4"];;
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    ALAssetsLibraryWriteVideoCompletionBlock completionBlock =
    ^(NSURL *savedURL, NSError *error) {
        if (error) {
            NSLog( @"Error while saving video Photo Library: %@", error );
        } else {
            NSLog( @"Successfuly saved video to Photo Library %@", savedURL.absoluteString);
        }
    };
    
    if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:videoURL])
    {
        [library writeVideoAtPathToSavedPhotosAlbum:videoURL completionBlock:completionBlock];
    }