What is the fastest way to extract all frames of video into images in C#?

Question

I have created a application to extract every frame from a video. It is not perfect yet and has a lot of problems with it. One of the problems is how long it takes. It took a full 2 hours to extract the frames of a 3 minutes video and the original video was four minutes but it gave me a memory error after the video was nearly finished:

'OpenCV: Failed to allocate 2764800 bytes'

so, it takes a long time to complete the task and it has a few bugs I am using Emgu.CV and MediaToolkit

Here is my code:

  using Emgu.CV;
  using MediaToolkit;
  using MediaToolkit.Model;



    string file;

    private void CreateFrames()
    {
        int i = 0;

        VideoCapture _video = new VideoCapture(file);
        var videoInfo = new MediaFile { Filename = file };
        using (var engine = new Engine()) { engine.GetMetadata(videoInfo); }

        while (i <= videoInfo.Metadata.Duration.Milliseconds * videoInfo.Metadata.VideoData.Fps)
        {
            Mat m = new Mat();
            _video.Read(m);
            _video.SetCaptureProperty(Emgu.CV.CvEnum.CapProp.PosFrames, i);
            preview.Image = _video.QueryFrame().ToBitmap();
            Bitmap bitmap = _video.QueryFrame().ToBitmap();
            bitmap.Save(String.Format(@"C:\\frames\\videoframe-{0}.png", i), 
    ImageFormat.Png);
            i++;
        }
    }

    private async void browse_Click(object sender, EventArgs e)
    {
        DialogResult result = openFileDialog.ShowDialog();
        if (result == DialogResult.OK)
        {
            file = openFileDialog.FileName;
            var videoInfo = new MediaFile { Filename = file };
            using (var engine = new Engine()) { engine.GetMetadata(videoInfo); }
            label1.Text = videoInfo.Metadata.VideoData.Fps + "  \n" + 
         videoInfo.Metadata.Duration.ToString();

            // must be run on a second thread else it will not work and it will freeze
            Task getframes = new Task(CreateFrames);
            getframes.Start();
        }
    }

I would appreciate if somebody has a solution to make this faster and possibly a fix to the memory problem.

Answer 1

First of all, check for IDisposable objects without the "using". For example, Bitmap inherits from Image, that implements IDisposable. So, when using the bimap, your code should be like this:

using (Bitmap bitmap = _video.QueryFrame().ToBitmap())
{
    bitmap.Save(String.Format(@"C:\\frames\\videoframe-{0}.png", i), ImageFormat.Png);
}

Also check if the Mat class implements IDisposable. If it is the case, another using could help you with the memory problem.

For the performance issue, I really cant help, but 3 minutes video, at 60fps, are 10800 frames. 2 hours are 7200 seconds. So 0.6 seconds per frame. Is this really slow? Just asking, I have no idea...