inabox/InABox.Mobile/InABox.Mobile.iOS/ImageToolsiOS.cs

using System;
using System.IO;
using AVFoundation;
using CoreGraphics;
using CoreMedia;
using Foundation;
using UIKit;

[assembly: Xamarin.Forms.Dependency(typeof(InABox.Mobile.iOS.ImageToolsiOS))]
namespace InABox.Mobile.iOS
{
    
    public class ImageToolsiOS : IImageTools
    {

        public byte[] CreateVideoThumbnail(byte[] video, float maxwidth, float maxheight)
        {
            byte[] result = null;
            var filename = Path.Combine(
                Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
                $"{Guid.NewGuid().ToString()}.tmp"
            );
            File.WriteAllBytes(filename,video);
            // perhaps? on IOS, try to use - NSUrl.FromFilename (path) instead of - new Foundation.NSUrl(url)
            var asset = AVAsset.FromUrl(NSUrl.FromFilename(filename));
            AVAssetImageGenerator imageGenerator = new AVAssetImageGenerator(asset);
            //AVAssetImageGenerator imageGenerator = new AVAssetImageGenerator(AVAsset.FromUrl((new Foundation.NSUrl(filename))));
            imageGenerator.AppliesPreferredTrackTransform = true;
            CMTime actualTime;
            NSError error;
            CGImage cgImage = imageGenerator.CopyCGImageAtTime(new CMTime(1, 1), out actualTime, out error);
            using (var ms = new MemoryStream())
            {
                var png = new UIImage(cgImage).AsPNG().AsStream();
                png.CopyTo(ms);
                result = ms.ToArray();
            }

            if (result != null)
                result = CreateThumbnail(result, maxwidth, maxheight);
            
            File.Delete(filename);
            return result;
        }
        
        public byte[] CreateThumbnail(byte[] source, float maxwidth, float maxheight)
        {
            byte[] result = { };
            using (UIImage src = UIImage.LoadFromData(NSData.FromArray(source)))
            {
                if (src != null)
                {
                    if ((src.Size.Width > 0.0F) && (src.Size.Height > 0.0F))
                    {
                        var maxFactor = Math.Min(maxwidth / src.Size.Width, maxheight / src.Size.Height);
                        var width = maxFactor * src.Size.Width;
                        var height = maxFactor * src.Size.Height;
                        UIGraphics.BeginImageContextWithOptions(new CGSize((float)width, (float)height), true, 1.0f);
                        src.Draw(new CGRect(0, 0, (float)width, (float)height));
                        var tgt = UIGraphics.GetImageFromCurrentImageContext();
                        UIGraphics.EndImageContext();

                        using (NSData imageData = tgt.AsJPEG())
                        {
                            result = new byte[imageData.Length];
                            System.Runtime.InteropServices.Marshal.Copy(imageData.Bytes, result, 0,
                                Convert.ToInt32(imageData.Length));
                        }
                    }
                }
            }
            return result;
        }
    }
}