Question

我正在制作一款录制视频的iOS应用，然后对该视频进行一些处理以创建另一个视频文件。我从videoCapture获得了非常奇怪的行为。它的作用就像文件已被打开但get（）调用似乎为我关心的所有属性返回1（我知道它们不是1）。我的代码如下所示：

VideoCapture cap(fileIn); // open the video file for reading

if ( !cap.isOpened() )  // if not success, exit program
  {
    cout << "Cannot open the video file" << endl;
    return -1;
  }
  else{
    cout << "File Open " << fileIn << endl;
  }

  double dFps = cap.get(CV_CAP_PROP_FPS); //get the frames per seconds of the video
  cout << "Frames per second = " << dFps << endl;

  double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
  double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video
  cout << "Frame Size = " << dWidth << "x" << dHeight << endl;

  Size frameSize(static_cast<int>(dWidth), static_cast<int>(dHeight));

  double dFrameCount = cap.get(CV_CAP_PROP_FRAME_COUNT);
  cout << "Frame count = " << dFrameCount << endl;

  VideoWriter oVideoWriter (fileOut, CV_FOURCC('m','p', '4', 'v'), dFps, frameSize, true); //initialize the VideoWriter object

  if ( !oVideoWriter.isOpened() ) //if not initialize the VideoWriter successfully, exit the program
  {
    cout << "ERROR: Failed to write the video" << endl;
    return -1;
  }
  else{
    cout << "Output file open." << endl;
  }

，控制台输出为：

File Open /var/mobile/Containers/Data/Application/7CEE8B87-BD50-4172-8F62-A74AD7F3C45A/Documents/15318B74-07D9-43EE-932F-224EDCA9CDA7.mov
Frames per second = 1
Frame Size = 1x1
Frame count = 1
Output file open.

我尝试将文件路径更改为无效文件，以防它根本找不到该文件，但这给了我“无法打开视频文件”。任何想法，将不胜感激。我认为这可能是一个权限问题，因为当我尝试使用此代码访问相机胶卷中的视频时，我看到了类似的行为，但此文件位于我的应用程序文档目录中，因此我应该可以完全访问它。

Answer 1

至少在最近两年（OpenCV on iOS - VideoCapture properties always return 1），这似乎是一个问题，并且iOS版本的视频捕捉根本不适用于打开文件。

我找到了另一种方法（使用apple apis打开视频，然后将每个帧转换为opencv Mat），但一般来说，opencv的iOS端口似乎远非完整且几乎完全没有记录。

Answer 2

首先，从UIImagePickerController对象获取视频文件的网址

   func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any])
{
    picker.dismiss(animated: true, completion: nil)

    let url = info[UIImagePickerController.InfoKey.mediaURL] as? NSURL
    let asset   = AVURLAsset.init(url: url! as URL)


    let mainstoryBoard = UIStoryboard(name:"Main", bundle: nil)
    let viewcontroller = mainstoryBoard.instantiateViewController(withIdentifier:"ViewController") as! ViewController
    viewcontroller.url = url
    viewcontroller.asset = asset
    self.navigationController?.pushViewController(viewcontroller, animated: true)


}

然后，使用该网址发送到cvwrapper.mm文件，如openVideoFile函数所示

- (void)openVideoFile:(NSURL *)fileName {

NSString *filename = fileName.path;
std::string filePath = [filename UTF8String];

cv::VideoCapture capture(filePath);

if (!capture.isOpened()) {
    printf("@Error Opening video file");
    // failed, print error message
}
else {
    printf("File Opened");
}

}

OpenCV videoCapture为iOS应用文档目录

2 个答案: