Video length - image array to video

Question

I posted a question earlier but didn't get the correct solution. May be I was not very clear about the question Frame Duration time - UIImage array to movie thats why I repeat this

I am working on a project where I need to export video from UIImage array. My array contains 4 images and I want every image will be shown for 5 seconds that means the video length will be 20 seconds. But my exported video length is 25 seconds and first image is showing for 10 seconds and last 3 images is showing for 15 seconds (5 seconds each). So, last 3 images are working perfectly. I was trying this code...

var outputSize = CGSize(width: 1920, height: 1280)

func build(outputSize outputSize: CGSize) {
        let fileManager = NSFileManager.defaultManager()
        let urls = fileManager.URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
        guard let documentDirectory: NSURL = urls.first else {
            fatalError("documentDir Error")
        }
        let videoOutputURL = documentDirectory.URLByAppendingPathComponent("OutputVideo.mp4")
       if NSFileManager.defaultManager().fileExistsAtPath(videoOutputURL!.path!) {
            do {
                try NSFileManager.defaultManager().removeItemAtPath(videoOutputURL!.path!)
            } catch {
                fatalError("Unable to delete file: \(error) : \(#function).")
            }
        }
        guard let videoWriter = try? AVAssetWriter(URL: videoOutputURL!, fileType: AVFileTypeMPEG4) else {
            fatalError("AVAssetWriter error")
        }
        let outputSettings = [AVVideoCodecKey : AVVideoCodecH264, AVVideoWidthKey : NSNumber(float: Float(outputSize.width)), AVVideoHeightKey : NSNumber(float: Float(outputSize.height))]
        guard videoWriter.canApplyOutputSettings(outputSettings, forMediaType: AVMediaTypeVideo) else {
            fatalError("Negative : Can't apply the Output settings...")
        }
        let videoWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: outputSettings)
        let sourcePixelBufferAttributesDictionary = [kCVPixelBufferPixelFormatTypeKey as String : NSNumber(unsignedInt: kCVPixelFormatType_32ARGB), kCVPixelBufferWidthKey as String: NSNumber(float: Float(outputSize.width)), kCVPixelBufferHeightKey as String: NSNumber(float: Float(outputSize.height))]
        let pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: videoWriterInput, sourcePixelBufferAttributes: sourcePixelBufferAttributesDictionary)
        if videoWriter.canAddInput(videoWriterInput) {
            videoWriter.addInput(videoWriterInput)
        }
        if videoWriter.startWriting() {
        videoWriter.startSession(atSourceTime: kCMTimeZero)
        assert(pixelBufferAdaptor.pixelBufferPool != nil)
        let media_queue = DispatchQueue(label: "mediaInputQueue")
        videoWriterInput.requestMediaDataWhenReady(on: media_queue, using: { () -> Void in
            let fps: Int32 = 1
            let framePerSecond: Int64 = 5
            let frameDuration = CMTimeMake(framePerSecond, fps)
            var frameCount: Int64 = 0
            var appendSucceeded = true
            while (!self.choosenPhotos.isEmpty) { //choosenPhotos is image array
                if (videoWriterInput.isReadyForMoreMediaData) {
                    let nextPhoto = self.choosenPhotos.remove(at: 0)
                    let lastFrameTime = CMTimeMake(frameCount * framePerSecond, fps)
                    let presentationTime = frameCount == 0 ? lastFrameTime : CMTimeAdd(lastFrameTime, frameDuration)
                    print("presentationTime-------------\(presentationTime)")
                    var pixelBuffer: CVPixelBuffer? = nil
                    let status: CVReturn = CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, pixelBufferAdaptor.pixelBufferPool!, &pixelBuffer)
                    if let pixelBuffer = pixelBuffer, status == 0 {
                        let managedPixelBuffer = pixelBuffer
                        CVPixelBufferLockBaseAddress(managedPixelBuffer, CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))
                        let data = CVPixelBufferGetBaseAddress(managedPixelBuffer)
                        let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
                        let context = CGContext(data: data, width: Int(self.outputSize.width), height: Int(self.outputSize.height), bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(managedPixelBuffer), space: rgbColorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue)
                        context!.clear(CGRect(x: 0, y: 0, width: CGFloat(self.outputSize.width), height: CGFloat(self.outputSize.height)))
                        let horizontalRatio = CGFloat(self.outputSize.width) / nextPhoto.size.width
                        let verticalRatio = CGFloat(self.outputSize.height) / nextPhoto.size.height
                        //aspectRatio = max(horizontalRatio, verticalRatio) // ScaleAspectFill
                        let aspectRatio = min(horizontalRatio, verticalRatio) // ScaleAspectFit
                        let newSize: CGSize = CGSize(width: nextPhoto.size.width * aspectRatio, height: nextPhoto.size.height * aspectRatio)
                        let x = newSize.width < self.outputSize.width ? (self.outputSize.width - newSize.width) / 2 : 0
                        let y = newSize.height < self.outputSize.height ? (self.outputSize.height - newSize.height) / 2 : 0
                        context?.draw(nextPhoto.cgImage!, in: CGRect(x: x, y: y, width: newSize.width, height: newSize.height))
                        CVPixelBufferUnlockBaseAddress(managedPixelBuffer, CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))
                        appendSucceeded = pixelBufferAdaptor.append(pixelBuffer, withPresentationTime: presentationTime)
                    } else {
                        print("Failed to allocate pixel buffer")
                        appendSucceeded = false
                    }
                }
                if !appendSucceeded {
                    break
                }
                frameCount += 1
            }
            videoWriterInput.markAsFinished()
            videoWriter.finishWriting { () -> Void in
                self.imageArrayToVideoComplete = true
                print("Image array to mutable video complete :)")
            }
        })
    }
}

Actually I am a bit confused about the variable presentationTime. For this reason I printed that and in Xcode, output log was like this

presentationTime-------------CMTime(value: 0, timescale: 1, flags: __C.CMTimeFlags(rawValue: 1), epoch: 0)
presentationTime-------------CMTime(value: 10, timescale: 1, flags: __C.CMTimeFlags(rawValue: 1), epoch: 0)
presentationTime-------------CMTime(value: 15, timescale: 1, flags: __C.CMTimeFlags(rawValue: 1), epoch: 0)
presentationTime-------------CMTime(value: 20, timescale: 1, flags: __C.CMTimeFlags(rawValue: 1), epoch: 0)

here the first value is 0 and second value is 10 - difference is 10. But from the second presentationTime, it is working great (value is increasing by 5). I guess this is the problem. What is the minimal change I need to do ?

Answer 1

Try to simplify your code, instead of:

 let lastFrameTime = CMTimeMake(frameCount * framePerSecond, fps)
    let presentationTime = frameCount == 0 ? lastFrameTime : CMTimeAdd(lastFrameTime, frameDuration)

just do as follows:

let presentationTime = CMTimeMake(frameCount * framePerSecond, fps)

Answer 2

Just comment out in this line in the buildVideoFromImageArray function after

//            videoWriter.startSession(atSourceTime: kCMTimeZero)

And add the following lines in its place

        let zeroTime = CMTimeMake(Int64(self.reloadDurationFromSlideShow),Int32(1))
        videoWriter.startSession(atSourceTime: zeroTime)

Tested it out. You also test it out and let me know.