MyApp/VisualCueExport.swift

1import AVFoundation2import UIKit3import CoreImage4 5@MainActor6enum VisualCueExport {7    static func export(raw: URL, cue: VisualCue, timing: CueTiming, to destination: URL) async throws {8        let asset = AVURLAsset(url: raw)9        let duration = try await asset.load(.duration)10        guard timing.start.isFinite, timing.duration.isFinite, timing.start >= 0, timing.duration > 0,11              timing.start + timing.duration <= duration.seconds,12              !(try await asset.loadTracks(withMediaType: .video)).isEmpty else {13            throw PartyError.message("Visual cue timing or video is unavailable.")14        }15        // Rasterize only the neutral badge once; AVFoundation provides upright source frames.16        let format = UIGraphicsImageRendererFormat()17        format.scale = 118        let renderer = UIGraphicsImageRenderer(size: CGSize(width: 512, height: 512), format: format)19        let badge = renderer.image { _ in20            UIColor.black.withAlphaComponent(0.85).setFill()21            UIBezierPath(roundedRect: CGRect(x: 0, y: 0, width: 512, height: 512), cornerRadius: 76).fill()22            let attributes: [NSAttributedString.Key: Any] = [23                .font: UIFont.systemFont(ofSize: 384, weight: .black), .foregroundColor: UIColor.white24            ]25            let text = cue.letter as NSString26            let size = text.size(withAttributes: attributes)27            text.draw(at: CGPoint(x: (512 - size.width) / 2, y: (512 - size.height) / 2), withAttributes: attributes)28        }29        guard let cgImage = badge.cgImage else { throw PartyError.message("Could not render visual cue.") }30        let overlay = CIImage(cgImage: cgImage)31        let start = timing.start32        let end = timing.start + timing.duration33        let composition = try await AVVideoComposition(applyingFiltersTo: asset) { parameters in34            let source = parameters.sourceImage35            let time = parameters.compositionTime.seconds36            guard time >= start && time < end else {37                return AVCIImageFilteringResult(resultImage: source, ciContext: nil)38            }39            let bounds = source.extent40            let side = min(bounds.width, bounds.height) * 0.4441            let scaled = overlay.transformed(by: CGAffineTransform(scaleX: side / 512, y: side / 512))42            let positioned = scaled.transformed(by: CGAffineTransform(translationX: bounds.midX - side / 2, y: bounds.midY - side / 2))43            return AVCIImageFilteringResult(resultImage: positioned.composited(over: source).cropped(to: bounds), ciContext: nil)44        }45        guard let exporter = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetHighestQuality) else {46            throw PartyError.message("Visual cue export is unavailable.")47        }48        exporter.videoComposition = composition49        // Preserve microphone audio, including the original action; never announce the letter.50        try await exporter.export(to: destination, as: .mp4)51    }52}