iOS 应用 Display Recorder 如何在不使用私有 API 的情况下录制屏幕

IOS

IOS 应用 Display Recorder 是一款功能强大的屏幕录制应用程序，它可以在不使用私有 API 的情况下录制屏幕。接下来，我们将介绍如何实现屏幕录制的功能，并提供案例代码供参考。

屏幕录制的原理

在 IOS 平台上，要实现屏幕录制的功能，需要使用到 Core Media 和 AV Foundation 框架。Core Media 提供了底层的媒体处理功能，而 AV Foundation 则提供了高级的媒体操作接口。

录制屏幕的步骤

1. 创建一个 AVAssetWriter 对象，用于将屏幕录制的内容写入到文件中。

2. 创建一个 AVAssetWriterInput 对象，并将其添加到 AVAssetWriter 对象中。AVAssetWriterInput 对象用于接收屏幕录制的内容。

3. 获取屏幕的分辨率和刷新率，并根据这些参数创建一个 AVAssetWriterInputPixelBufferAdaptor 对象。AVAssetWriterInputPixelBufferAdaptor 对象用于将屏幕录制的内容转换成像素数据。

4. 创建一个 CADisplayLink 对象，并将其添加到主运行循环中。CADisplayLink 对象用于定时获取屏幕的内容。

5. 在 CADisplayLink 的回调方法中，获取屏幕的内容，并将其写入到 AVAssetWriterInputPixelBufferAdaptor 对象中。

示例代码

下面是一个简单的示例代码，演示如何在 IOS 应用中录制屏幕：

Swift
import UIKit
import AVFoundation
class ScreenRecorder {
    private var assetWriter: AVAssetWriter?
    private var assetWriterInput: AVAssetWriterInput?
    private var pixelBufferAdaptor: AVAssetWriterInputPixelBufferAdaptor?
    private var displayLink: CADisplayLink?
    
    func startRecording() {
        let screenSize = UIScreen.mAIn.bounds.size
        let outputFileURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("screenRecording.mp4")
        
        do {
            assetWriter = try AVAssetWriter(url: outputFileURL, fileType: .mp4)
            
            let outputSettings = [
                AVVIDEOCodecKey: AVVIDEOCodecType.h264,
                AVVIDEOWidthKey: screenSize.width,
                AVVIDEOHeightKey: screenSize.height
            ] as [String : Any]
            
            assetWriterInput = AVAssetWriterInput(mediaType: .vIDEO, outputSettings: outputSettings)
            assetWriterInput?.expectsMediaDatAInRealTime = true
            
            let pixelBufferAttributes = [
                kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32ARGB,
                kCVPixelBufferWidthKey as String: screenSize.width,
                kCVPixelBufferHeightKey as String: screenSize.height
            ] as [String : Any]
            
            pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: assetWriterInput!, sourcePixelBufferAttributes: pixelBufferAttributes)
            
            assetWriter?.add(assetWriterInput!)
            
            displayLink = CADisplayLink(target: self, selector: #selector(captureScreen))
            displayLink?.add(to: .mAIn, forMode: .default)
            
            assetWriter?.startWriting()
            assetWriter?.startSession(atSourceTime: .zero)
        } catch {
            print("FAIled to start screen recording: \(error)")
        }
    }
    
    @objc private func captureScreen() {
        guard let assetWriterInput = assetWriterInput, assetWriterInput.isReadyForMoreMediaData else {
            return
        }
        
        guard let pixelBufferPool = pixelBufferAdaptor?.pixelBufferPool else {
            return
        }
        
        let pixelBuffer = createPixelBuffer(from: UIScreen.mAIn)
        pixelBufferAdaptor?.append(pixelBuffer, withPresentationTime: .zero)
    }
    
    private func createPixelBuffer(from view: UIView) -> CVPixelBuffer? {
        let screenSize = UIScreen.mAIn.bounds.size
        let scale = UIScreen.mAIn.scale
        
        UIGraphicsBeginImageContextWithOptions(screenSize, false, scale)
        
        guard let context = UIGraphicsGetcurrentContext() else {
            return nil
        }
        
        view.layer.render(in: context)
        
        guard let image = UIGraphicsGetImageFromCurrentImageContext()?.cgImage else {
            return nil
        }
        
        UIGraphicsEndImageContext()
        
        var pixelBuffer: CVPixelBuffer?
        let status = CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &pixelBuffer)
        
        if status != kCVReturnSuccess {
            return nil
        }
        
        CVPixelBufferLockBaseAddress(pixelBuffer!, .readOnly)
        
        let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer!)
        let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer!)
        let bytesPerPixel = 4
        
        let context = CGContext(
            data: pixelData,
            width: Int(screenSize.width),
            height: Int(screenSize.height),
            bitsPerComponent: 8,
            bytesPerRow: bytesPerRow,
            space: CGColorSpaceCreateDeviceRGB(),
            bitmapInfo: CGImageAlphAInfo.noneSkipFirst.rawValue
        )
        
        context?.draw(image, in: CGRect(x: 0, y: 0, width: screenSize.width, height: screenSize.height))
        
        CVPixelBufferUnlockBaseAddress(pixelBuffer!, .readOnly)
        
        return pixelBuffer
    }
    
    func stopRecording() {
        displayLink?.invalidate()
        displayLink = nil
        
        assetWriterInput?.markAsFinished()
        assetWriter?.finishWriting {
            if self.assetWriter?.status == .completed {
                // 屏幕录制完成
            } else {
                // 屏幕录制失败
            }
        }
    }
}

参考文章

- [AVFoundation Programming Guide](Apple.com/library/archive/documentation/AudioVIDEO/Conceptual/AVFoundationPG/Articles/00_Introduction.html">https://developer.Apple.com/library/archive/documentation/AudioVIDEO/Conceptual/AVFoundationPG/Articles/00_Introduction.html)

- [AVAssetWriter](https://developer.Apple.com/documentation/avfoundation/avassetwriter)

- [CADisplayLink](https://developer.Apple.com/documentation/quartzcore/CADisplaylink)