首先我应该提到我是新的（iOS 和 Xamarin）。我正在尝试使用图像和文本为视频添加水印。
我已经从链接中移植了大部分代码：https ://stackoverflow.com/a/22016800/5275669 。
整个代码粘贴在这里：
try {
var videoAsset = AVUrlAsset.FromUrl (new NSUrl (filepath, false)) as AVUrlAsset;
AVMutableComposition mixComposition = AVMutableComposition.Create ();
var compositionVideoTracks = mixComposition.AddMutableTrack (AVMediaType.Video, 0);
AVAssetTrack clipVideoTrack = videoAsset.TracksWithMediaType (AVMediaType.Video) [0];
var compositionAudioTrack = mixComposition.AddMutableTrack (AVMediaType.Audio, 0);
AVAssetTrack clipAudioTrack = videoAsset.TracksWithMediaType (AVMediaType.Audio) [0];
NSError error;
CMTimeRange timeRangeInAsset = new CMTimeRange ();
timeRangeInAsset.Start = CMTime.Zero;
timeRangeInAsset.Duration = videoAsset.Duration;
compositionVideoTracks.InsertTimeRange (timeRangeInAsset, clipVideoTrack, CMTime.Zero, out error);
compositionVideoTracks.InsertTimeRange (timeRangeInAsset, clipAudioTrack, CMTime.Zero, out error);
compositionVideoTracks.PreferredTransform = clipVideoTrack.PreferredTransform;
CGSize sizeOfVideo = videoAsset.NaturalSize;
CATextLayer textOfvideo = (CATextLayer)CATextLayer.Create ();
textOfvideo.String = String.Format ("{0} {1}", DateTime.Now.ToLongTimeString (), "Test app");
textOfvideo.SetFont (CGFont.CreateWithFontName ("Helvetica"));
textOfvideo.FontSize = 50;
textOfvideo.AlignmentMode = CATextLayer.AlignmentCenter;
textOfvideo.Frame = new CGRect (0, 0, sizeOfVideo.Width, sizeOfVideo.Height / 6);
textOfvideo.ForegroundColor = new CGColor (255, 0, 0);
UIImage myImage = UIImage.FromFile ("Icon-Small.png");
CALayer layerCa = CALayer.Create ();
layerCa.Contents = myImage.CGImage;
layerCa.Frame = new CGRect (0, 0, 100, 100);
layerCa.Opacity = 0.65F;
CALayer optionalLayer = CALayer.Create ();
optionalLayer.AddSublayer (textOfvideo);
optionalLayer.Frame = new CGRect (0, 0, sizeOfVideo.Width, sizeOfVideo.Height);
optionalLayer.MasksToBounds = true;
CALayer parentLayer = CALayer.Create ();
CALayer videoLayer = CALayer.Create ();
parentLayer.Frame = new CGRect (0, 0, sizeOfVideo.Width, sizeOfVideo.Height);
videoLayer.Frame = new CGRect (0, 0, sizeOfVideo.Width, sizeOfVideo.Height);
parentLayer.AddSublayer (videoLayer);
parentLayer.AddSublayer (layerCa);
parentLayer.AddSublayer (textOfvideo);
AVMutableVideoComposition videoComposition = AVMutableVideoComposition.Create ();
videoComposition.RenderSize = sizeOfVideo;
videoComposition.FrameDuration = new CMTime (1, 30);
videoComposition.AnimationTool = AVVideoCompositionCoreAnimationTool.FromLayer (videoLayer, parentLayer);
AVMutableVideoCompositionInstruction instruction = AVMutableVideoCompositionInstruction.Create () as AVMutableVideoCompositionInstruction;
CMTimeRange timeRangeInstruction = new CMTimeRange ();
timeRangeInstruction.Start = CMTime.Zero;
timeRangeInstruction.Duration = mixComposition.Duration;
instruction.TimeRange = timeRangeInstruction;
AVAssetTrack videoTrack = mixComposition.TracksWithMediaType (AVMediaType.Video) [0];
AVMutableVideoCompositionLayerInstruction layerInstruction = AVMutableVideoCompositionLayerInstruction.FromAssetTrack (videoTrack);
instruction.LayerInstructions = new AVVideoCompositionLayerInstruction[] { layerInstruction };
List<AVVideoCompositionInstruction> instructions = new List<AVVideoCompositionInstruction> ();
instructions.Add (instruction);
videoComposition.Instructions = instructions.ToArray ();
var exportSession = new AVAssetExportSession (mixComposition, AVAssetExportSession.PresetMediumQuality);
exportSession.VideoComposition = videoComposition;
Console.WriteLine ("Original path is {0}", filepath);
string newFileName = Path.GetFileName (filepath);
newFileName = newFileName.Replace (".mp4", "_wm.mp4");
string directoryName = Path.GetDirectoryName (filepath);
string videoOutFilePath = Path.Combine (directoryName, newFileName);
Console.WriteLine ("New path is {0}", videoOutFilePath);
exportSession.OutputFileType = AVFileType.Mpeg4;
exportSession.OutputUrl = NSUrl.FromFilename (videoOutFilePath);
exportSession.ShouldOptimizeForNetworkUse = true;
exportSession.ExportAsynchronously (() => {
AVAssetExportSessionStatus status = exportSession.Status;
Console.WriteLine ("Done with handler. Status: " + status.ToString ());
switch (status) {
case AVAssetExportSessionStatus.Completed:
Console.WriteLine ("Sucessfully Completed");
if (File.Exists (videoOutFilePath)) {
Console.WriteLine ("Created!!");
} else
Console.WriteLine ("Failed");
break;
case AVAssetExportSessionStatus.Cancelled:
break;
case AVAssetExportSessionStatus.Exporting:
break;
case AVAssetExportSessionStatus.Failed:
Console.WriteLine ("Task failed => {0}", exportSession.Error);
Console.WriteLine (exportSession.Error.Description);
break;
case AVAssetExportSessionStatus.Unknown:
break;
case AVAssetExportSessionStatus.Waiting:
break;
default:
break;
}
});
if (File.Exists (videoOutFilePath))
return videoOutFilePath;
} catch (Exception ex) {
Console.WriteLine ("Error occured : {0}", ex.Message);
}
我不断收到以下错误：任务失败=>无法完成导出错误域=AVFoundationErrorDomain代码=-11820“无法完成导出”用户信息=0x18896070 {NSLocalizedRecoverySuggestion=再次尝试导出。，NSLocalizedDescription=无法完成导出}
如果我替换这个
var exportSession = new AVAssetExportSession (mixComposition, AVAssetExportSession.PresetMediumQuality);
和
var exportSession = new AVAssetExportSession (videoAsset, AVAssetExportSession.PresetMediumQuality);
它工作正常，但没有水印
有人能帮忙吗？？