iOS AVFoundation - Show a time display over a video and export

I want to show a display o开发者_StackOverflow社区verlay over a video and export that video including this display. I had a look into the AVFoundation Framework, AVCompositions, AVAssets etc. but I still do not have an idea to achieve this. There is a class called AVSynchronizedLayer which lets you animate things synchrounous to the video, but I do not want to animate, I jsut want to overlay the time display into every single frame of the video. Any advice?

Regards

Something like this...

(NB: culled from a much larger project, so I may have included some unnecessary pieces by accident).

You'll need to grab the CALayer of your clock / animation, and set it to the var myClockLayer (used 1/3 of the way down by the andimation tool).

This also assumes your incoming video has just two tracks - audio and video. If you have more, you'll need to set the track id in "asTrackID:2" more carefully.

AVURLAsset* url = [AVURLAsset URLAssetWithURL:incomingVideo options:nil];
AVMutableComposition *videoComposition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionVideoTrack = [videoComposition  addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *clipVideoTrack = [[url tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [url duration])  ofTrack:clipVideoTrack atTime:kCMTimeZero error:&error];

AVMutableVideoComposition* videoComposition = [[AVMutableVideoComposition videoComposition]retain];
videoComposition.renderSize = CGSizeMake(320, 240);
videoComposition.frameDuration = CMTimeMake(1, 30);
videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithAdditionalLayer:myClockLayer asTrackID:2];

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30) );

AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];

videoComposition.instructions = [NSArray arrayWithObject: instruction];

exporter = [[AVAssetExportSession alloc] initWithAsset:saveComposition presetName:AVAssetExportPresetHighestQuality] ;
exporter.videoComposition = videoComposition;
exporter.outputURL=url3;
exporter.outputFileType=AVFileTypeQuickTimeMovie;

[exporter exportAsynchronouslyWithCompletionHandler:^(void){}];

I think you can use AVCaptureVideoDataOutput to process each frame and use AVAssetWriter to record the processed frame.You can refer to this answer

https://stackoverflow.com/a/4944594/379941 .

use AVAssetWriterPixelBufferAdaptor's appendPixelBuffer:withPresentationTime: method to export
And I strongly suggest using OpenCV to process frame. this is a nice tutorial

http://aptogo.co.uk/2011/09/opencv-framework-for-ios/.

OpenCV library is very great.