Applying a CIFilter to a Video File and Saving it

Question

Is there any fast, lightweight-as-possible way to apply a CIFilter to a video? Before it's mentioned, I have looked at GPUImage - it looks like very powerful magic code, but it's really overkill for what I'm trying to do.

Essentially, I would like to

1. Take a video file, say stored at /tmp/myVideoFile.mp4
2. Apply a CIFilter to this video file
3. Save the video file to a different (or the same) location, say /tmp/anotherVideoFile.mp4

I've been able to apply a CIFilter to a video that's playing extremely easily and quickly using AVPlayerItemVideoOutput

let player = AVPlayer(playerItem: AVPlayerItem(asset: video))
let output = AVPlayerItemVideoOutput(pixelBufferAttributes: nil)
player.currentItem?.addOutput(self.output)
player.play()

let displayLink = CADisplayLink(target: self, selector: #selector(self.displayLinkDidRefresh(_:)))
displayLink.addToRunLoop(NSRunLoop.mainRunLoop(), forMode: NSRunLoopCommonModes)

func displayLinkDidRefresh(link: CADisplayLink){
    let itemTime = output.itemTimeForHostTime(CACurrentMediaTime())
    if output.hasNewPixelBufferForItemTime(itemTime){
        if let pixelBuffer = output.copyPixelBufferForItemTime(itemTime, itemTimeForDisplay: nil){
            let image = CIImage(CVPixelBuffer: pixelBuffer)
            // apply filters to image
            // display image
        }
    }
}

This works great, but I've been having a lot just the tiniest bit of trouble finding out how to apply a filter to an already saved video file. There is the option of basically just doing what I did above, using an AVPlayer, playing the video, and getting the pixel buffer from every frame as it is played but this won't work for video processing in the background. I don't think users would appreciate having to wait as long as their video is for the filter to be applied.

In way over-simplified code, I'm looking for something like this:

var newVideo = AVMutableAsset() // We'll just pretend like this is a thing

var originalVideo = AVAsset(url: NSURL(urlString: "/example/location.mp4"))
originalVideo.getAllFrames(){(pixelBuffer: CVPixelBuffer) -> Void in
    let image = CIImage(CVPixelBuffer: pixelBuffer)
        .imageByApplyingFilter("Filter", withInputParameters: [:])

    newVideo.addFrame(image)
}

newVideo.exportTo(url: NSURL(urlString: "/this/isAnother/example.mp4"))

Is there any way fast (again, not involving GPUImage, and ideally working in iOS 7) way to apply a filter to a video file and then save it? For example this would take a saved video, load it into an AVAsset, apply a CIFilter, and then save the new video to a different location.

Answer 1

In iOS 9 / OS X 10.11 / tvOS, there's a convenience method for applying CIFilters to video. It works on an AVVideoComposition, so you can use it both for playback and for file-to-file import/export. See AVVideoComposition.init(asset:applyingCIFiltersWithHandler:) for the method docs.

There's an example in Apple's Core Image Programming Guide, too:

let filter = CIFilter(name: "CIGaussianBlur")!
let composition = AVVideoComposition(asset: asset, applyingCIFiltersWithHandler: { request in

    // Clamp to avoid blurring transparent pixels at the image edges
    let source = request.sourceImage.clampingToExtent()
    filter.setValue(source, forKey: kCIInputImageKey)

    // Vary filter parameters based on video timing
    let seconds = CMTimeGetSeconds(request.compositionTime)
    filter.setValue(seconds * 10.0, forKey: kCIInputRadiusKey)

    // Crop the blurred output to the bounds of the original image
    let output = filter.outputImage!.cropping(to: request.sourceImage.extent)

    // Provide the filter output to the composition
    request.finish(with: output, context: nil)
})

That part sets up the composition. After you've done that, you can either play it by assigning it to an AVPlayer or write it to a file with AVAssetExportSession. Since you're after the latter, here's an example of that:

let export = AVAssetExportSession(asset: asset, presetName: AVAssetExportPreset1920x1200)
export.outputFileType = AVFileTypeQuickTimeMovie
export.outputURL = outURL
export.videoComposition = composition

export.exportAsynchronouslyWithCompletionHandler(/*...*/)

There's a bit more about this in the WWDC15 session on Core Image, starting around 20 minutes in.

---

If you want a solution that works on earlier OS, it's a bit more complicated.

^{Aside: Think about how far back you really need to support. As of August 15, 2016, 87% of devices are on iOS 9.0 or later, and 97% are on iOS 8.0 or later. Going to a lot of effort to support a small slice of your potential customer base—and it'll get even smaller by the time you get your project done and ready to deploy—might not be worth the cost.}

There are a couple of ways to go at this. Either way, you'll be getting CVPixelBuffers representing source frames, creating CIImages from them, applying filters, and rendering out new CVPixelBuffers.

1. Use AVAssetReader and AVAssetWriter to read and write pixel buffers. There's examples for how to do this (the reading and writing part; you still need to do the filtering in between) in the Export chapter of Apple's AVFoundation Programming Guide.

2. Use AVVideoComposition with a custom compositor class. Your custom compositor is given AVAsynchronousVideoCompositionRequest objects that provide access to pixel buffers and a way for you to provide processed pixel buffers. Apple has a sample code project called AVCustomEdit that shows how to do this (again, just the getting and returning sample buffers part; you'd want to process with Core Image instead of using their GL renderers).

Of those two, the AVVideoComposition route is more flexible, because you can use a composition both for playback and export.