Webcam Fetcher Application

Here's the source code for a little console application that I built to automatically download the current image from a webcam so that you can build a directory full of stills (with the goal of later animating the stills to get one of those time-lapsed [fast-moving] movies).

I'm not sure if Carl's going to appreciate the drain on his bandwidth, but the DNR webcam URL is hardcoded in this code.

FWIW: I created this app originally so that I could capture Mount Saint Helens erupting last year. I dusted it off again last night because I'd like to see if I can later merge the GPS/mapping data from the roadtrip with the archived webcam images.

This code performs a couple of tricks:

1. It automatically adjusts the interval between downloads between a minimum value (10 seconds here) and a maximum value (10 minutes). This way, when the webcam is turned off, you don't continue to flood the web server with requests for the exact same picture. As soon as a new frame is detected, the interval resets to the minimum so that you don't miss any more of the action.

2. It uses a hash value on the image to see if it was the same as the previously retrieved image (in which case, the application does not save the current image).

class Class1
{
   private static readonly int MINIMUM_WAIT = 10000;
   private static readonly int MAXIMUM_WAIT = 600000;
   private static int _CURRENT_WAIT = 10000;


   [STAThread]
   static void Main(string[] args)
   {
      for (;;)
      {
         FetchIt();
         System.Threading.Thread.Sleep(_CURRENT_WAIT);
      }
   }


   static void FetchIt()
   {
      WebClient web = new WebClient();


      string hash1 = "";
      string hash2 = "";


      System.Security.Cryptography.MD5CryptoServiceProvider hasher = 
         new System.Security.Cryptography.MD5CryptoServiceProvider();


      if (System.IO.File.Exists(@"c:\dnr\latest.jpg"))
      {
         System.IO.FileStream fs = 
            System.IO.File.OpenRead(@"c:\dnr\latest.jpg");


         byte[] hash = hasher.ComputeHash(fs);


         fs.Close();


         foreach (byte b in hash)
            hash1 += b.ToString("X2");
      }


      try
      {
         web.DownloadFile(
            @"http://www.dotnetrocks.com/roadtrip/cam/webcam.jpg?random=" + 
            new Random().Next(9999999).ToString(), @"c:\dnr\latest.jpg");


         System.IO.FileStream fs = System.IO.File.OpenRead(@"c:\dnr\latest.jpg");


         byte[] hash = hasher.ComputeHash(fs);


         long len = fs.Length;


         fs.Close();


         foreach (byte b in hash)
            hash2 += b.ToString("X2");


         if (hash1 != hash2 && len > 12000)
         {
            _CURRENT_WAIT = MINIMUM_WAIT;


            string fn = @"c:\dnr\" + 
               DateTime.Now.ToString("yyyyMMddHHmmss") + ".jpg";


            Console.WriteLine(fn + " " + len.ToString());


            System.IO.File.Copy(@"c:\dnr\latest.jpg", fn);
         }
         else
         {
            _CURRENT_WAIT += (3 * MINIMUM_WAIT);


            if (_CURRENT_WAIT > MAXIMUM_WAIT)
               _CURRENT_WAIT = MAXIMUM_WAIT;
         }
      }
      catch (Exception)
      {}
      finally
      {
         web = null;
      }
   }
}