从 AVPlayer 中提取位图非常不确定

Posted 2023-02-19

【中文标题】从 AVPlayer 中提取位图非常不确定

【英文标题】：Extracting bitmap from AVPlayer is very uncertain

【发布时间】：2021-12-13 07:52:37

【问题描述】：

我想在某个时间点从视频播放器中提取UIIMage，并对该图像进行一些处理。

我有这个代码：

pausePlayer()
let time = player!.currentTime() 
imageFromVideo(url: fileURL(for: movieName!), at: time.seconds)  image in
let result = self.detectLines(image: image!    
if let result = result 
    // Display results by handing off to the InferenceViewController.
    DispatchQueue.main.async 
        self.drawNewResults(result: result)
    

        

和

public func imageFromVideo(url: URL, at time: TimeInterval, completion: @escaping (UIImage?) -> Void) 
    DispatchQueue.global(qos: .background).async 
        let asset = AVURLAsset(url: url)

        let assetIG = AVAssetImageGenerator(asset: asset)
        assetIG.appliesPreferredTrackTransform = true
        assetIG.apertureMode = AVAssetImageGenerator.ApertureMode.encodedPixels
        let cmTime = CMTime(seconds: time, preferredTimescale: CMTimeScale(30.0))
        var newTime = CMTime(seconds: time, preferredTimescale: CMTimeScale(30.0))
        let thumbnailImageRef: CGImage

        do 
            thumbnailImageRef = try assetIG.copyCGImage(at: cmTime, actualTime: &newTime)
         catch let error 
            print("Error: \(error)")
            return completion(nil)
        
        print("Time on click: %f", cmTime.seconds)
        print("Actual time: %f",  newTime.seconds)

        DispatchQueue.main.async 
            completion(UIImage(cgImage: thumbnailImageRef))
        
    

问题是我想要图像的时间和我得到的图像之间存在巨大差距。通常它类似于 0.2s 和 0.4s，大约是 7 14 帧之间的偏移量。所以我做和展示的处理是错误的，因为我没有处理观察到的图像。

例子：

Time on click: %f 0.8333333333333334
Actual time: %f 1.0666666666666667

Time on click: %f 1.6333333333333333
Actual time: %f 2.1666666666666665

【参考方案1】：

这里建议：swift: How to take screenshot of AVPlayerLayer()

assetIG.requestedTimeToleranceAfter = CMTime.zero
assetIG.requestedTimeToleranceBefore = CMTime.zero

成功了。