I have been spending time trying to figure out how to crop and zoom a specific video based on user input from a scrollview.

Imagine we have a zoomable view (works for images and videos). This includes a scrollview and an av player layer. Users can zoom and pan around within the view which will be cropped later.

I am able to calculate the crop area and reposition the video within a mutable composition, however I can’t seem to “fit” the video within the render size without losing quality.

Below is the code I am currently using with a few screenshots.

        let size = videoMutableTrack.naturalSize.applying(videoMutableTrack.preferredTransform)
        
        var scaleRatioX = (renderSize.width / 2) / currentVideoView.contentSize.width
        var scaleRatioY = (renderSize.height) / currentVideoView.contentSize.height
        if (rotate) {
            scaleRatioX = (renderSize.width) / currentVideoView.contentSize.width
            scaleRatioY = (renderSize.height / 2) / currentVideoView.contentSize.height
        }

        let scale = CGAffineTransform(scaleX: scaleRatioX, y: scaleRatioY) // When using this scale, no zoom is applied.
        
        let scale = CGAffineTransform(scaleX: scaleRatioX * (currentVideoView.zoomScale / 2), y: scaleRatioY * (currentVideoView.zoomScale / 2)) // When using this scale, zoom is applied (last screenshot)
        
        let offsetX = -currentVideoView.contentOffset.x
        let offsetY = -currentVideoView.contentOffset.y
        
        let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoMutableTrack)

        let move = CGAffineTransform(translationX: offsetX, y: offsetY)

        layerInstruction.setTransform(move.concatenating(scale), at: .zero)

        let mutableVideoComposition = AVMutableVideoComposition()
        mutableVideoComposition.instructions = [compositionInstruction]
        mutableVideoComposition.frameDuration = CMTimeMake(value: 1, timescale: Int32(highestFrameRate))
        mutableVideoComposition.renderSize = renderSize
        mutableVideoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: outputLayer)