Michiel Michiel - 7 months ago 194
Objective-C Question

How can I add a watermark in a captured video on iOS

I was wondering if anybody can tell me how I can achieve this. If been thinking of a couple of solutions:

  1. Create individual images from the captured video and later merge them per image and after that create a new AVAsset... Sounds a bit complicated don't you think?

  2. Merge 2 videos, one is transparent (the one holding the watermark) and the other is the asset captured with the camera.


Adding a watermark is quite more simple. You just need to use a CALayer and AVVideoCompositionCoreAnimationTool. The code can be just copied and assembled in the same order. I have just tried to insert some comments in between for better understanding.

Let's assume you recorded the video already so we are going to create the AVURLAsset first:

AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:outputFileURL options:nil];
AVMutableComposition* mixComposition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo  preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) 
                            atTime:kCMTimeZero error:nil];

[compositionVideoTrack setPreferredTransform:[[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] preferredTransform]]; 

With just this code you would be able to export the video but we want to add the layer with the watermark first. Please note that some code may seem redundant but it is necessary for everything to work.

First we create the layer with the watermark image:

UIImage *myImage = [UIImage imageNamed:@"icon.png"];
CALayer *aLayer = [CALayer layer];
aLayer.contents = (id)myImage.CGImage;
aLayer.frame = CGRectMake(5, 25, 57, 57); //Needed for proper display. We are using the app icon (57x57). If you use 0,0 you will not see it
aLayer.opacity = 0.65; //Feel free to alter the alpha here

If we don't want an image and want text instead:

CATextLayer *titleLayer = [CATextLayer layer];
titleLayer.string = @"Text goes here";
titleLayer.font = @"Helvetica";
titleLayer.fontSize = videoSize.height / 6;
//?? titleLayer.shadowOpacity = 0.5;
titleLayer.alignmentMode = kCAAlignmentCenter;
titleLayer.bounds = CGRectMake(0, 0, videoSize.width, videoSize.height / 6); //You may need to adjust this for proper display

The following code sorts the layer in proper order:

CGSize videoSize = [videoAsset naturalSize]; 
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];   
parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:aLayer];
[parentLayer addSublayer:titleLayer]; //ONLY IF WE ADDED TEXT

Now we are creating the composition and add the instructions to insert the layer:

AVMutableVideoComposition* videoComp = [[AVMutableVideoComposition videoComposition] retain];
videoComp.renderSize = videoSize;
videoComp.frameDuration = CMTimeMake(1, 30);
videoComp.animationTool = [AVVideoCompositionCoreAnimationTool      videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

/// instruction

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mixComposition duration]);
AVAssetTrack *videoTrack = [[mixComposition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];
videoComp.instructions = [NSArray arrayWithObject: instruction];

And now we are ready to export:

_assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetMediumQuality];//AVAssetExportPresetPassthrough   
_assetExport.videoComposition = videoComp;

NSString* videoName = @"mynewwatermarkedvideo.mov";

NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:videoName];
NSURL    *exportUrl = [NSURL fileURLWithPath:exportPath];

if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) 
[[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];

_assetExport.outputFileType = AVFileTypeQuickTimeMovie; 
_assetExport.outputURL = exportUrl;
_assetExport.shouldOptimizeForNetworkUse = YES;

[strRecordedFilename setString: exportPath];

[_assetExport exportAsynchronouslyWithCompletionHandler:
 ^(void ) {
 [_assetExport release];

[audioAsset release];
[videoAsset release];

As found on iPhone Watermark on recorded Video.