Get Image from Video

Question

I am trying to write an application which can access cameras connected to PC, record a video and get an image from the video. I use AForge.NET libraries to access cameras: http://www.aforgenet.com/framework/

I don't know how the event named AForge.Video.NewFrameEventHandler works. In this code the event returns null to a bitmap instead of a new frame from a video or the event is not called. I want to get frames from the video to a picture box every time frame to make something like a video stream and after click on the stop button I want the last image to stay displayed in the picture box. Does anyone know how? And why my code doesn't work?

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using AForge.Video.DirectShow;
using System.Drawing;
using AForge.Video;

namespace CameraDevice
{
    public class CameraImaging
    {
        // enumerate video devices
        public FilterInfoCollection videoDevices = new FilterInfoCollection(FilterCategory.VideoInputDevice );
        //camera
        public VideoCaptureDevice videoSource;
        //screen shot
        public Bitmap bitmap;
        public CameraImaging()
        {
            // create video source
            VideoCaptureDevice videoSource = new VideoCaptureDevice(videoDevices[0].MonikerString );
            // set NewFrame event handler
            videoSource.NewFrame += new NewFrameEventHandler( video_NewFrame );
        }
        public void StartVideo(VideoCaptureDevice videoSource)
        {
            // start the video source
            videoSource.Start();
            // ...
        }
        public void StopVideo(VideoCaptureDevice videoSource)
        {
            // stop the video source
            videoSource.Stop();
            // ...
        }
        private void video_NewFrame( object sender, NewFrameEventArgs eventArgs )
        {
            // get new frame
            bitmap = eventArgs.Frame;
            // process the frame
        }
    }
}

The similar code is here: http://www.aforgenet.com/framework/features/directshow_video.html[^]

In the Windows Forms I run this video in a thread which does this method:

private void VideoRecording()
    {
        camImg.videoSource.Start();

        while (!StopVideo)
        {
            pictureBox1.Image = camImg.bitmap;
            pictureBox1.Invalidate();
        }
        camImg.videoSource.Stop();

    }

Answer 1

If I remember correctly the bitmap needs to be copied right away since it is overwritten after the event. Using a reference is no good here. Try something like:

private void video_NewFrame( object sender, NewFrameEventArgs eventArgs )
{
    // copy the new frame
    bitmap = new Bitmap(eventArgs.Frame);
    // process the frame
}

or

private void video_NewFrame( object sender, NewFrameEventArgs eventArgs )
{
   // clone new frame
   bitmap = eventArgs.Frame.Clone();
   // process the frame
}

Also you should not use an extra thread for this, AForge already does that.

1. Call Start (e.g. in the load event, or after pressing a button)

2. Handle the frame events

   private void VideoStream_NewFrame(object sender, AForge.Video.NewFrameEventArgs eventArgs)
   {
       Bitmap newFrame = new Bitmap(eventArgs.Frame);
       pictureBox1.Image = newFrame;
   }
   

3. Call Stop (closing event or button)

If you run into issues with WinForm controls e.g. a label you need to know that these controls were created on another thread and you need to use Invoke. E.g:

label_ms.Invoke((MethodInvoker)(() => label_ms.Text = msTimeSpan.TotalMilliseconds.ToString()));

Your best bet is to check out this AForge sample that comes with the framework: http://aforge.googlecode.com/svn/trunk/Samples/Video/Player/