how to play back a slow motion video via URL in iOS?

I am trying to support video playback for remote video files in iOS. It works for a regular video, but has a problem with slow motion videos: the slow motion effect is lost. I.e. A slow motion plays back like a regular speed rate video.

Here is what I am doing:

        AVURLAsset *asset = [AVURLAsset URLAssetWithURL:url options:nil];
        [asset.resourceLoader setDelegate:self.urlDelegate
                                    queue:[self.urlDelegate getDispatchQueue]];

        AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:asset];
        AVPlayer *player = [AVPlayer playerWithPlayerItem:playerItem];
        AVPlayerViewController *controller = [[AVPlayerViewController alloc] init];

        controller.player = player;
        [player play];
        [self presentViewController:controller animated:false completion:^{
           <snipped>
        }];

Note, the url points to a QuickTime (.MOV) video file on a HTTP(s) server.

Again, the above code plays a slow motion video just like a regular video without any slow motions. Is it because AVURLAsset does not support slow motion video? What are I missing to let AVPlayer plays slow motion?

I am targeting iOS 12 and above.

Thanks!