How to record a video with C# – WPF and AForge

In this article we will see how to record a video and a snapshot from a camera (USB or IP camera), with C# and AForge.
AForge is a library used for image acquisition and Image Processing, for example to analyse images and detect objects with a Camera.

In a previous article, we already saw how to recognize shapes and colours from an image taken from a Camera in real time.
When using image processing, being able to record video and save screenshots is helpful to debug the application and understand what is happening with the image-processing algorithm.

Watch the video on YouTube

Download the FFmpeg library

To record a video you need a library called Accord.Video.FFmpeg. You can get it from NuGet.

This library is a mirror of AForge.Video.FFmpeg, which wasn’t deployed on NuGet because of the GPL license, which is different from all other AForge licenses (LGPL).

The license of FFMpeg is GPL or LGPL, depending on how it is compiled. You can read about the licensing here: https://www.ffmpeg.org/legal.html

To keep it short, it says that you can use the library for your business, but they can’t guarantee that the algorithms they use are not under copyright.

Recording the video: how to create a video file

To record a video you need two actions: Start recording and Stop recording.

When you start recording, you need to create a file with the class VideoFileWriter.
The file needs to know the height and width of the images that it’s going to store, so we will use the Image size that comes directly from the camera.

This is the code to create the video file:

private VideoFileWriter _writer;

...

_writer = new VideoFileWriter();
_writer.Open(dialog.FileName, (int)Math.Round(Image.Width, 0), 
              (int)Math.Round(Image.Height, 0));

If you need to specify the codecs used to compress the video, you can use one of the many overloads of the method Open. There is also the possibility to specify other parameters of the recording.

public void Open(string fileName, int width, int height);

public void Open(string fileName, int width, int height, int frameRate);

public void Open(string fileName, int width, int height, int frameRate, 
                 VideoCodec codec);

public void Open(string fileName, int width, int height, int frameRate, 
                 VideoCodec codec, int bitRate);

public void Open(string fileName, int width, int height, int frameRate, 
                 VideoCodec codec, int bitRate, AudioCodec audioCodec, 
                 int audioBitrate, int sampleRate, int channels);

How to add images to the video file

A video is just a quick succession of images displayed with the right timing. That’s why we have to add the images that we receive from the camera while recording the video.

Every time we add an image we have also to specify at what time this image has to be displayed.

We already saw in a previous article that AForge uses a callback mechanism to notify that a new image is arrived.

We will use the callback to add the images to the file.
The video starts when we add the first image, that’s why we have to store the time of the start in a variable.
When we receive more images from the camera and add them to the video, we also have to specify the time that we received them.

Here is the code used on the callback both for the first image and for consecutive ones:

try
{
    if (_recording)
    {
        if (_firstFrameTime != null)
        {
            _writer.WriteVideoFrame(eventArgs.Frame, DateTime.Now - _firstFrameTime.Value);
        }
        else
        {
            _writer.WriteVideoFrame(eventArgs.Frame);
            _firstFrameTime = DateTime.Now;
        }
    }
...

How to stop recording and close the video file

To stop the video, we have to save and close the file. We also must Dispose the VideoFileWriter to release the unmanaged resources.

Here is the code on how to stop the video:

private void StopRecording()
{
    _recording = false;
    _writer.Close();
    _writer.Dispose();
}

How to save a snapshot

When receiving a stream of images from a camera, it is also possible to save a single image.

To do this we just need to use WPF libraries and in particular PngBitmapEncoder class and BitmapFrame.Create method.

Here is the code to save a WPF BitmapImage to a file:

var encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(Image));
using (var filestream = new FileStream(dialog.FileName, FileMode.Create))
{
encoder.Save(filestream);
}

Download the sample application

You can download the sample application on GitHub.