Converting slow motion video to an URL asset for upload

In the iOS application I currently work on the users can choose a video from the device’s gallery and that video gets uploaded to the backend.

This functionality has always worked fine but recently somebody tried to upload s slow motion video and the application was not able to handle it.

Turns out slow motion videos need a special case, they work a bit differently than normal videos.

When you pick a video from the device’s gallery you get a PHAsset of type .video. You can use PHImageManager to load it as AVAsset.

The application just tried to cast it to AVURLAsset and processed it as a video file stored at some url that can be converted to Data and uploaded to the backend.

A slow motion video is an AVAsset, just not an AVURLAsset but an AVComposition and it needs to be treated differently.

The best way to make it work for my upload to backend scenario was to export it to a standard video file

guard let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetMediumQuality) else {
    Log.error?.message("Could not create AVAssetExportSession")
    return
}

let targetURL = dataPathProvider.uploadsDirectory.appendingPathComponent("\(UUID().uuidString).mp4")

exportSession.outputURL = targetURL
exportSession.outputFileType = AVFileType.mp4
exportSession.shouldOptimizeForNetworkUse = true

exportSession.exportAsynchronously {
    let exportedAsset = AVURLAsset(url: targetURL)
    self.processVideoAsset(asset: exportedAsset)
}

After the slow motion video gets exported it can be converted to an AVURLAsset and treated the same way as a normal video file.

Just make sure you set the correct extension for the exported file as without it you will not be able to preview in AVPlayer or get the duration or thumbnail for it.