How to access NSData/NSURL of slow motion videos using PhotoKit

Question

Working with new Photo framework, I can access the NSData of PHAssets using requestImageDataForAsset. I can also access the file URL using the PHImageFileURLKey of the returned info NSDictionary.

[[PHImageManager defaultManager] requestImageDataForAsset:asset options:nil resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {

                //imageData contains the correct data for images and videos
                NSLog(@"info - %@", info);
                NSURL* fileURL = [info objectForKey:@"PHImageFileURLKey"];
}];

This works fine for images and normal videos.

However, when the asset is a PHAssetMediaSubtypeVideoHighFrameRate (slow motion video), the returned data corresponds to a JPG file containing the first frame of the video (both the NSData, the dataUTI and the info dictionary point to the same jpg file). As example, this is the URL and the dataUTI returned for a slow motion video:

PHImageFileURLKey = "file:///var/mobile/Media/PhotoData/Metadata/DCIM/100APPLE/IMG_0642.JPG"; PHImageFileUTIKey = "public.jpeg";

Why is this happening? How can i access the NSData/NSURL of the slow motion video instead of this JPG preview?

Answer 1

After going nuts and testing every single option I found the problem.

The responsable of returning JPG images for slow motion videos is the default PHImageRequestOptionsVersionCurrent value for the PHImageRequestOptions.version property.

Simply assign the version to PHImageRequestOptionsVersionUnadjusted or PHImageRequestOptionsVersionOriginal will return the original slow motion video.

PHImageRequestOptions * imageRequestOptions = [[PHImageRequestOptions alloc] init];

imageRequestOptions.version = PHImageRequestOptionsVersionUnadjusted;
// or 
imageRequestOptions.version = PHImageRequestOptionsVersionOriginal;

I consider this as an unexpected behaviour, since i am not expecting that the "current" version of a slow motion video is a still image (maybe a video with the slow motion effect applied, but not a photo).

Hope this is usefull to someone.

Answer 2

It is important to note that Slow motion videos are of type AVComposition not AVURLAsset. An AVComposition object combines media data from multiple sources together.

Exporting a slow motion video

To achieve this, I basically went through a three-step process:

1. Create an output URL for the video
2. Configure an export session
3. Export the video and grab the URL!

---

PHVideoRequestOptions *options = [PHVideoRequestOptions new];
        options.networkAccessAllowed = YES;
        [[PHImageManager defaultManager] requestAVAssetForVideo:asset options:options resultHandler:^(AVAsset *asset, AVAudioMix *audioMix, NSDictionary *info) {
            if(([asset isKindOfClass:[AVComposition class]] && ((AVComposition *)asset).tracks.count == 2)){
                //slow motion videos. See Here: https://overflow.buffer.com/2016/02/29/slow-motion-video-ios/

                //Output URL of the slow motion file.
                NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
                NSString *documentsDirectory = paths.firstObject;
                NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"mergeSlowMoVideo-%d.mov",arc4random() % 1000]];
                NSURL *url = [NSURL fileURLWithPath:myPathDocs];

                //Begin slow mo video export
                AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];
                exporter.outputURL = url;
                exporter.outputFileType = AVFileTypeQuickTimeMovie;
                exporter.shouldOptimizeForNetworkUse = YES;

                [exporter exportAsynchronouslyWithCompletionHandler:^{
                    dispatch_async(dispatch_get_main_queue(), ^{
                        if (exporter.status == AVAssetExportSessionStatusCompleted) {
                            NSURL *URL = exporter.outputURL;
                            self.filePath=URL.absoluteString;



                            // NSData *videoData = [NSData dataWithContentsOfURL:URL];
                            //
                            //// Upload
                            //[self uploadSelectedVideo:video data:videoData];
                        }
                    });
                }];


            } 
        }];

Please see this wonderful blog for slow motion videos in iOS.