I have a Swift class that takes an image and creates a 10 second video of this image.
I am creating a video using AVAssetWriter . It displays the video in ten seconds. All this works as expected.
func setup(){ //Setup video size self.videoSize = self.getVideoSizeForImage(self.videoImage!) //Setup temp video path self.tempVideoPath = self.getTempVideoPath() //Setup video writer var videoWriter = AVAssetWriter( URL: NSURL(fileURLWithPath: self.tempVideoPath!), fileType: AVFileTypeMPEG4, error: nil) //Setup video writer input let videoSettings = [ AVVideoCodecKey: AVVideoCodecH264, AVVideoWidthKey: self.videoSize!.width, AVVideoHeightKey: self.videoSize!.height ] let videoWriterInput = AVAssetWriterInput( mediaType: AVMediaTypeVideo, outputSettings: videoSettings as [NSObject : AnyObject] ) videoWriterInput.expectsMediaDataInRealTime = true //Setup video writer adaptor let adaptor = AVAssetWriterInputPixelBufferAdaptor( assetWriterInput: videoWriterInput, sourcePixelBufferAttributes: [ kCVPixelBufferPixelFormatTypeKey : kCVPixelFormatType_32ARGB, ] ) videoWriter.addInput(videoWriterInput) //Setup frame time self.currentFrameTime = CMTimeMake(0, 10000) //Start video writing session videoWriter.startWriting() videoWriter.startSessionAtSourceTime(self.currentFrameTime!) self.currentVideoWriter = videoWriter self.currentVideoWriterAdaptor = adaptor } func addImageToVideoWriter(image:UIImage, duration:CGFloat){ //Get image pixel buffer let buffer = self.pixelBufferFromImage(image) var frameTime = self.currentFrameTime! //Add pixel buffer to video let adaptor = self.currentVideoWriterAdaptor! while(!adaptor.assetWriterInput.readyForMoreMediaData){} if adaptor.assetWriterInput.readyForMoreMediaData{ adaptor.appendPixelBuffer( buffer, withPresentationTime: frameTime ) let seconds = CGFloat(CMTimeGetSeconds(frameTime))+duration var timescale = frameTime.timescale var value = CGFloat(timescale) * seconds frameTime.value = Int64(value) frameTime.timescale = Int32(timescale) self.currentFrameTime = frameTime self.lastImage = image } } func pixelBufferFromImage(image:UIImage) -> CVPixelBufferRef{ let size = image.size var pixelBuffer: Unmanaged<CVPixelBuffer>? let bufferOptions:CFDictionary = [ "kCVPixelBufferCGBitmapContextCompatibilityKey": NSNumber(bool: true), "kCVPixelBufferCGImageCompatibilityKey": NSNumber(bool: true) ] let status:CVReturn = CVPixelBufferCreate( nil, Int(size.width), Int(size.height), OSType(kCVPixelFormatType_32ARGB), bufferOptions, &pixelBuffer ) let managedPixelBuffer = pixelBuffer!.takeRetainedValue() let lockStatus = CVPixelBufferLockBaseAddress(managedPixelBuffer, 0) let pixelData = CVPixelBufferGetBaseAddress(managedPixelBuffer) let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedFirst.rawValue) let rgbColorSpace = CGColorSpaceCreateDeviceRGB() let context = CGBitmapContextCreate( pixelData, Int(size.width), Int(size.height), 8, Int(4 * size.width), rgbColorSpace, bitmapInfo ) CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), image.CGImage) CVPixelBufferUnlockBaseAddress(managedPixelBuffer, 0) return managedPixelBuffer } func saveVideoWriterToDisk(){ self.addImageToVideoWriter(self.lastImage!, duration: 0) self.currentVideoWriter?.endSessionAtSourceTime(self.currentFrameTime!) self.currentVideoWriterAdaptor?.assetWriterInput.markAsFinished() //Write video to disk let semaphore = dispatch_semaphore_create(0) self.currentVideoWriter?.finishWritingWithCompletionHandler({ dispatch_semaphore_signal(semaphore) }) dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER) }
Then I use AVAssetExportSession and AVMutableComposition to add music to this video. This works most of the time.
func exportVideo(sourceFilePath:String, destinationFilePath:String) -> Bool{ let fileManager = NSFileManager() var success = false //Compile audio and video together let composition = AVMutableComposition() /* //Setup audio track let trackAudio:AVMutableCompositionTrack = composition.addMutableTrackWithMediaType( AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID() ) //Add audio file to audio track let audioFileAsset = AVURLAsset(URL:self.audioFileURL, options:nil) let audioFileAssetTrack = audioFileAsset.tracksWithMediaType(AVMediaTypeAudio).last as! AVAssetTrack trackAudio.insertTimeRange( audioFileAssetTrack.timeRange, ofTrack: audioFileAssetTrack, atTime: kCMTimeZero, error: nil )*/ //Setup video track let trackVideo:AVMutableCompositionTrack = composition.addMutableTrackWithMediaType( AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID() ) //Add video file to video track let videoFileAsset = AVURLAsset(URL: NSURL(fileURLWithPath: sourceFilePath), options: nil) let videoFileAssetTracks = videoFileAsset.tracksWithMediaType(AVMediaTypeVideo) if videoFileAssetTracks.count > 0{ let videoFileAssetTrack:AVAssetTrack = videoFileAssetTracks[0] as! AVAssetTrack trackVideo.insertTimeRange( videoFileAssetTrack.timeRange, ofTrack: videoFileAssetTrack, atTime: kCMTimeZero, error: nil ) } //Export compiled video to disk if fileManager.fileExistsAtPath(destinationFilePath){ fileManager.removeItemAtPath(destinationFilePath, error: nil) } let exporter = AVAssetExportSession( asset: composition, presetName: AVAssetExportPresetHighestQuality ) exporter.outputFileType = AVFileTypeMPEG4 exporter.outputURL = NSURL(fileURLWithPath: destinationFilePath) let semaphore = dispatch_semaphore_create(0) exporter.exportAsynchronouslyWithCompletionHandler({ success = true dispatch_semaphore_signal(semaphore) }) dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER) //Delete file at source path fileManager.removeItemAtPath(sourceFilePath, error: nil) return success }
But.
When the image is quite large (in terms of resolution, that is 1600 * 1600 or more), the video created using AVAssetExportSession is 8 seconds instead of 10. The time difference only occurs when using large images.
This is not a huge problem. Since it is unlikely that people will use this class with large images. However, I would still like to know what is happening and how to fix it.