video-to-gif.swift

import UIKit
import AVFoundation
import Photos
import MobileCoreServices

class ViewController: UIViewController {
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
    
        startVideoToGIFProcess()
    }
    
    func startVideoToGIFProcess() {
        // Download the video and write it to temp storage
        print("Downloading video…")
        let data = try! Data(contentsOf: URL(string: "https://i.imgur.com/dXxP7a9.mp4")!)
        let fileName = String(format: "%@_%@", ProcessInfo.processInfo.globallyUniqueString, "html5gif.mp4")
        let fileURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(fileName)
        try! data.write(to: fileURL, options: [.atomic])
        
        createGIF(fromVideoAtURL: fileURL)
    }
    
    func createGIF(fromVideoAtURL url: URL) {
        print("Downloaded!")
        
        let frameRate: Int = 20
        let duration: TimeInterval = 9.68
        let totalFrames = Int(duration * TimeInterval(frameRate))
        let delayBetweenFrames: TimeInterval = 1.0 / TimeInterval(frameRate)
        
        var timeValues: [NSValue] = []
        
        for frameNumber in 0 ..< totalFrames {
            let seconds = TimeInterval(delayBetweenFrames) * TimeInterval(frameNumber)
            let time = CMTime(seconds: seconds, preferredTimescale: Int32(NSEC_PER_SEC))
            timeValues.append(NSValue(time: time))
        }
        
        let asset = AVURLAsset(url: url)
        let generator = AVAssetImageGenerator(asset: asset)
        generator.requestedTimeToleranceBefore = CMTime(seconds: 0.05, preferredTimescale: 600)
        generator.requestedTimeToleranceAfter = CMTime(seconds: 0.05, preferredTimescale: 600)
        
        let sizeModifier: CGFloat = 0.1
        generator.maximumSize = CGSize(width: 450.0 * sizeModifier, height: 563.0 * sizeModifier)
        
        // Set up resulting image
        let fileProperties: [String: Any] = [
            kCGImagePropertyGIFDictionary as String: [
                kCGImagePropertyGIFLoopCount as String: 0
            ]
        ]
        
        let frameProperties: [String: Any] = [
            kCGImagePropertyGIFDictionary as String: [
                kCGImagePropertyGIFDelayTime: delayBetweenFrames
            ]
        ]

        let resultingFilename = String(format: "%@_%@", ProcessInfo.processInfo.globallyUniqueString, "html5gif.gif")
        let resultingFileURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(resultingFilename)
        let destination = CGImageDestinationCreateWithURL(resultingFileURL as CFURL, kUTTypeGIF, totalFrames, nil)!
        CGImageDestinationSetProperties(destination, fileProperties as CFDictionary)
        
        print("Converting to GIF…")
        var framesProcessed = 0
        let startTime = CFAbsoluteTimeGetCurrent()
        
        generator.generateCGImagesAsynchronously(forTimes: timeValues) { (requestedTime, resultingImage, actualTime, result, error) in
            guard let resultingImage = resultingImage else { return }
            
            framesProcessed += 1
            
            CGImageDestinationAddImage(destination, resultingImage, frameProperties as CFDictionary)
            
            if framesProcessed == totalFrames {
                let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
                print("Done converting to GIF! Frames processed: \(framesProcessed) • Total time: \(timeElapsed) s.")
                
                // Save to Photos just to check…
                let result = CGImageDestinationFinalize(destination)
                print("Did it succeed?", result)
                
                if result {
                    print("Saving to Photos…")

                    PHPhotoLibrary.shared().performChanges({
                        PHAssetCreationRequest.creationRequestForAssetFromImage(atFileURL: resultingFileURL)
                    }) { (saved, err) in
                        print("Saved?", saved)
                    }
                }
            }
        }
    }
}

Nice, thank you so much!

Sorry, one more question - will this work for very large GIFs (ie over a minute)?

@bl791 I looked in Apollo and I have this code, so I'm going to guess right around a minute should be the maximum otherwise iOS will probably run out of memory due to GIFs being a very inefficient video storage format:

/// If the video is any longer than this, do not offer to save it as a GIF
static var upperLimitDurationThresholdForGIF: TimeInterval = 65.0

Thanks!