Swift – Compressing video files

This extension focuses on exporting it to a lower quality setting (in this case Medium) and uses an mp4 container, over the mov container favored by iOS. This can result in a loss of quality, but you can experiment with higher output settings and different formats as you work to fine tune your output.

extension PreviewVideoViewController: AVCaptureFileOutputRecordingDelegate {
    func fileOutput(_ output: AVCaptureFileOutput,
                    didFinishRecordingTo outputFileURL: URL,
                    from connections: [AVCaptureConnection],
                    error: Error?) {
        guard let data = try? Data(contentsOf: outputFileURL) else {
            return
        }

        print("File size before compression: \(Double(data.count / 1048576)) mb")

        let compressedURL = NSURL.fileURL(withPath: NSTemporaryDirectory() + UUID().uuidString + ".mp4")
        compressVideo(inputURL: outputFileURL as URL,
                      outputURL: compressedURL) { exportSession in
            guard let session = exportSession else {
                return
            }

            switch session.status {
            case .unknown:
                break
            case .waiting:
                break
            case .exporting:
                break
            case .completed:
                guard let compressedData = try? Data(contentsOf: compressedURL) else {
                    return
                }

                print("File size after compression: \(Double(compressedData.count / 1048576)) mb")
            case .failed:
                break
            case .cancelled:
                break
            }
        }
    }


    func compressVideo(inputURL: URL,
                       outputURL: URL,
                       handler:@escaping (_ exportSession: AVAssetExportSession?) -> Void) {
        let urlAsset = AVURLAsset(url: inputURL, options: nil)
        guard let exportSession = AVAssetExportSession(asset: urlAsset,
                                                       presetName: AVAssetExportPresetMediumQuality) else {
            handler(nil)

            return
        }

        exportSession.outputURL = outputURL
        exportSession.outputFileType = .mp4
        exportSession.exportAsynchronously {
            handler(exportSession)
        }
    }
}