How would I put together a video using the AVAssetWriter in swift?

Question

I'm currently making a small app that timelapses the webcam on my mac, saves the captured frame to png, and I am looking into exporting the captured frames as a single video.

I use CGImage to handle the original images and have them set in an array but I'm unsure on there to go from there. I gather from my own research that I have to use AVAssetWriter and AVAssetWriterInput somehow.

I've had a look about on here, read the apple docs and searched google. But all the guides etc, are in obj-c rather than swift which is making it really difficult to understand (As I have no experience in Obj-C).

Any help would be very much appreciated.

Many Thanks, Luke.

Chinookan

Answer 1

I solved the same problem in Swift. Starting from an array oh UIImage, try this (it's a little long :-) but works):

var choosenPhotos: [UIImage] = [] *** your array of UIImages ***
var outputSize = CGSizeMake(1280, 720)

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.startSessionAtSourceTime(kCMTimeZero)
        assert(pixelBufferAdaptor.pixelBufferPool != nil)

        let media_queue = dispatch_queue_create("mediaInputQueue", nil)

        videoWriterInput.requestMediaDataWhenReadyOnQueue(media_queue, usingBlock: { () -> Void in
            let fps: Int32 = 1
            let frameDuration = CMTimeMake(1, fps)

            var frameCount: Int64 = 0
            var appendSucceeded = true

            while (!self.choosenPhotos.isEmpty) {
                if (videoWriterInput.readyForMoreMediaData) {
                    let nextPhoto = self.choosenPhotos.removeAtIndex(0)
                    let lastFrameTime = CMTimeMake(frameCount, fps)
                    let presentationTime = frameCount == 0 ? lastFrameTime : CMTimeAdd(lastFrameTime, frameDuration)

                    var pixelBuffer: CVPixelBuffer? = nil
                    let status: CVReturn = CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, pixelBufferAdaptor.pixelBufferPool!, &pixelBuffer)

                    if let pixelBuffer = pixelBuffer where status == 0 {
                        let managedPixelBuffer = pixelBuffer

                        CVPixelBufferLockBaseAddress(managedPixelBuffer, 0)

                        let data = CVPixelBufferGetBaseAddress(managedPixelBuffer)
                        let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
                        let context = CGBitmapContextCreate(data, Int(self.outputSize.width), Int(self.outputSize.height), 8, CVPixelBufferGetBytesPerRow(managedPixelBuffer), rgbColorSpace, CGImageAlphaInfo.PremultipliedFirst.rawValue)

                        CGContextClearRect(context, CGRectMake(0, 0, CGFloat(self.outputSize.width), 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 = CGSizeMake(nextPhoto.size.width * aspectRatio, 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

                        CGContextDrawImage(context, CGRectMake(x, y, newSize.width, newSize.height), nextPhoto.CGImage)

                        CVPixelBufferUnlockBaseAddress(managedPixelBuffer, 0)

                        appendSucceeded = pixelBufferAdaptor.appendPixelBuffer(pixelBuffer, withPresentationTime: presentationTime)
                    } else {
                        print("Failed to allocate pixel buffer")
                        appendSucceeded = false
                    }
                }
                if !appendSucceeded {
                    break
                }
                frameCount++
            }
            videoWriterInput.markAsFinished()
            videoWriter.finishWritingWithCompletionHandler { () -> Void in
                print("FINISHED!!!!!")
            }
        })
    }
}

Corwin

I have a problem with this in iOS 8.4 building in Xcode 7.1. Works fine in iOS 9 but the callback from videoWriter.finishWritingWithCompletionHandler is never called. – Trapes

videoWriter.finishWritingWithCompletionHandler { () -> Void in let _ = videoWriter print("FINISHED!!!!!") } solves my problem – Trapes

where did you find the documentation to know how to use all this? I find the apple docs are so sparse – Pelton

Answer 2

Following is code to generate video from images working in Xcode 11.3.1 and Swift 5.1. This code is generated from the answer of @aleciufs Sep 25 '15 answer. The following function assumes the images are loaded and available var images array [UIImage]

func build(outputSize: CGSize) {
    let fileManager = FileManager.default
    let urls = fileManager.urls(for: .cachesDirectory, in: .userDomainMask)
    guard let documentDirectory = urls.first else {
        fatalError("documentDir Error")
    }

    let videoOutputURL = documentDirectory.appendingPathComponent("OutputVideo.mp4")

    if FileManager.default.fileExists(atPath: videoOutputURL.path) {
        do {
            try FileManager.default.removeItem(atPath: videoOutputURL.path)
        } catch {
            fatalError("Unable to delete file: \(error) : \(#function).")
        }
    }

    guard let videoWriter = try? AVAssetWriter(outputURL: videoOutputURL, fileType: AVFileType.mp4) else {
        fatalError("AVAssetWriter error")
    }

    let outputSettings = [AVVideoCodecKey : AVVideoCodecType.h264, AVVideoWidthKey : NSNumber(value: Float(outputSize.width)), AVVideoHeightKey : NSNumber(value: Float(outputSize.height))] as [String : Any]

    guard videoWriter.canApply(outputSettings: outputSettings, forMediaType: AVMediaType.video) else {
        fatalError("Negative : Can't apply the Output settings...")
    }

    let videoWriterInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: outputSettings)
    let sourcePixelBufferAttributesDictionary = [
        kCVPixelBufferPixelFormatTypeKey as String : NSNumber(value: kCVPixelFormatType_32ARGB),
        kCVPixelBufferWidthKey as String: NSNumber(value: Float(outputSize.width)),
        kCVPixelBufferHeightKey as String: NSNumber(value: Float(outputSize.height))
    ]
    let pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: videoWriterInput, sourcePixelBufferAttributes: sourcePixelBufferAttributesDictionary)

    if videoWriter.canAdd(videoWriterInput) {
        videoWriter.add(videoWriterInput)
    }

    if videoWriter.startWriting() {
        videoWriter.startSession(atSourceTime: CMTime.zero)
        assert(pixelBufferAdaptor.pixelBufferPool != nil)

        let media_queue = DispatchQueue(__label: "mediaInputQueue", attr: nil)

        videoWriterInput.requestMediaDataWhenReady(on: media_queue, using: { () -> Void in
            let fps: Int32 = 2
            let frameDuration = CMTimeMake(value: 1, timescale: fps)

            var frameCount: Int64 = 0
            var appendSucceeded = true

            while (!self.images.isEmpty) {
                if (videoWriterInput.isReadyForMoreMediaData) {
                    let nextPhoto = self.images.remove(at: 0)
                    let lastFrameTime = CMTimeMake(value: frameCount, timescale: fps)
                    let presentationTime = frameCount == 0 ? lastFrameTime : CMTimeAdd(lastFrameTime, frameDuration)

                    var pixelBuffer: CVPixelBuffer? = nil
                    let status: CVReturn = CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, pixelBufferAdaptor.pixelBufferPool!, &pixelBuffer)

                    if let pixelBuffer = pixelBuffer, status == 0 {
                        let managedPixelBuffer = pixelBuffer

                        CVPixelBufferLockBaseAddress(managedPixelBuffer, [])

                        let data = CVPixelBufferGetBaseAddress(managedPixelBuffer)
                        let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
                        let context = CGContext(data: data, width: Int(outputSize.width), height: Int(outputSize.height), bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(managedPixelBuffer), space: rgbColorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue)

                        context?.clear(CGRect(x: 0, y: 0, width: outputSize.width, height: outputSize.height))

                        let horizontalRatio = CGFloat(outputSize.width) / nextPhoto.size.width
                        let verticalRatio = CGFloat(outputSize.height) / nextPhoto.size.height

                        let aspectRatio = min(horizontalRatio, verticalRatio) // ScaleAspectFit

                        let newSize = CGSize(width: nextPhoto.size.width * aspectRatio, height: nextPhoto.size.height * aspectRatio)

                        let x = newSize.width < outputSize.width ? (outputSize.width - newSize.width) / 2 : 0
                        let y = newSize.height < outputSize.height ? (outputSize.height - newSize.height) / 2 : 0

                        context?.draw(nextPhoto.cgImage!, in: CGRect(x: x, y: y, width: newSize.width, height: newSize.height))

                        CVPixelBufferUnlockBaseAddress(managedPixelBuffer, [])

                        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
                print("FINISHED!!!!!")
                saveVideoToLibrary(videoURL: videoOutputURL)
            }
        })
    }
}

The extra function I provide is:

func saveVideoToLibrary(videoURL: URL) {

    PHPhotoLibrary.shared().performChanges({
        PHAssetChangeRequest.creationRequestForAssetFromVideo(atFileURL: videoURL)
    }) { saved, error in

        if let error = error {
            print("Error saving video to librayr: \(error.localizedDescription)")
        }
        if saved {
            print("Video save to library")

        }
    }
}

Agostino