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Image Pull tutorial

Image Pull is the name given to Webcam32's ability to stream images directly to a Netscape  or Internet Explorer browser connected to a web page.

This section provides a step-by-step tutorial with samples on setting up a web page to use Image Pull.  To get the most out of this tutorial, review the Image Pull documentation for Webcam32 here.  Don't worry if it seems too complicated at first, the purpose of this tutorial is to simplify the setup and usage.  After you have used it for a while, you will realize that it is not as difficult as it may have initially seemed.

 

Part 1 - The idea

This part describes the principles of how Image Pull works.  Reading this section makes clear the tutorial steps that will be followed in other parts.  For the impatient, you may jump directly to Part 2 if needed.  If you encounter problems, please come back and read this section.

Image Pull  is one of two primary techniques within Webcam32 to achieve streaming video.  Streaming video is the ability to have images within a web page continuously update as fast as possible presenting the appearance of real-time video.

Webcam32 is able to provide this function by continuously capturing a new, still frame (image) from the video capture device and sending that image to the browser.  As Webcam32 sends frame after frame, the appearance to the end user at the browser is that of a continuously updated video.

When a user at a browser surfs to a web page which is configured to use the Image Pull technique of Webcam32, the page is downloaded to the browser.  Inside the page, coded as part of the HTML is a small program written in a language called JavaScript.  This language is interpreted by the browser while the page is being displayed.  The JavaScript program determines the type of browser being used to view the page.

If the browser is the Netscape browser, one action is taken.  If the browser is Internet Explorer, a different action is taken.

  Browser type is Netscape

A Netscape browser natively supports a technology called Server Push.  Server Push is the ability for a web server or other source of data to continuously push data to the browser and the browser will automatically update the display.  Webcam32 is able to serve Server Push images directly to a Netscape browser and no further action is needed.  For more details on Server Push, see here.

  Browser type is Internet Explorer

Unfortunately, Internet Explorer does not support Server Push so an alternative technique is required when the Internet Explorer browser type is detected.  Fortunately, such a technique is available ... this is the heart of Image Pull.

The Image Pull technique works with additional JavaScript in the HTML of the page.  An HTML tag contained within the page is is directed to Webcam32 to obtain a single image.  The

You don't have to understand the details of the coding of the JavaScript in order to use Image Pull.  The JavaScript that is included in the page can be found in the sample contained in this tutorial.  Just make certain that any additional HTML that you add to the page does not interfere with the coding of the other JavaScript.

In order for the browser to form a connection to Webcam32 to receive the stream of images, the Image Pull page must know how to connect to Webcam32 to receive the images.  This is achieved by coding into the HTML of the web page, the TCP/IP address of the computer running Webcam32.

Lets read that again, this is where the majority of mistakes occur when configuring Image Pull.

The HTML of the Web page must contain the TCP/IP address of  the computer running Webcam32.

What is a TCP/IP address?

When someone calls you on the telephone, that person needs to know your telephone number.  TCP/IP addresses are the telephone numbers of the Internet.  When you wish to contact a remote computer from your PC, your PC needs to know the TCP/IP address of the machine that you wish to contact.  TCP/IP addresses are written in a format like 209.132.50.16.  This is 4 decimal numbers separated by a period (".").

When you or I make a telephone call, we normally remember or have written down a telephone number and dial it immediately.  But what if we don't know the number of someone we wish to call?  The answer is that we can look it up in the telephone book or call the operator.  How would you find the telephone number for your local cinema?

On the Internet, a service called the Domain Name System or DNS performs this lookup of TCP/IP addresses for us.  Instead of having to remember the, meaningless, TCP/IP addresses, we remember the names of computers on the Internet such as www.surveyorcorp.com.  When we refer to a name such as this (called the domain name), inside the computer, it is internally converted to its corresponding TCP/IP address.

For fun (some fun huh?) open a DOS window and enter the command:

PING WWW.SURVEYORCORP.COM

You will then see the TCP/IP address of the computer known as www.surveyorcorp.com.  Try some other computers, for example www.yahoo.com or www.microsoft.com).

By telling the HTML of the web page containing the Image Pull technique your TCP/IP address, the page can then contact your PC directly and start requesting images from Webcam32.

Each and every computer connected to the Internet has a TCP/IP address.  When you connect to the Internet, you too have a unique TCP/IP address.  For the majority of users reading this, you will use the services of an Internet Service Provider or ISP.  The ISP is the company from which you buy Internet access.  Whenever you dial the ISP provided telephone number from your computer's modem, the ISP dynamically assigns your PC a new TCP/IP address.  This means that each and every time you connect to the Internet from your PC, the chances are high that you will get a new TCP/IP address, different from the one that was assigned to you the last time you connected.

Webcam32 can be configured to modify the web page containing the Image Pull each time Webcam32 is started.  This ensures that even if the TCP/IP address of your PC has changed, the web page will contain the correct reference to your PC.

Sound simple enough?  In fact it is this simple ... in principle.  The challenge of Image Pull is getting the parameters correct.  Next we provide a tutorial for setup.

Part 2 - Setup

Setup of Image Pull comes in two parts.

Setup of Webcam32

Setup of Webcam32 involves installing the product.  This is covered elsewhere in the Webcam32 documentation.

To setup Webcam32 for Image Pull requires opening the TCP/IP settings dialog of Webcam32.  This can be done either by pressing the TCP/IP button on the toolbar ...   Alternatively, selecting File, then Preferences, and then TCP/IP from the menu will achieve the same result.

The following dialog will appear.

Within the dialog, we need to ensure that:

Features:

Access:

After changing these, press OK for the changes to take effect.

Setup of the Web page

To setup the tutorial web test web page, you must download the following ZIP file:

Sample Image Pull tutorial page

Create a folder (directory) on your PC to hold the contents of the ZIP file.  For this tutorial, we suggest C:\ImagePull

Extract the contents of the downloaded ZIP file into this folder.

The folder should now contain the following files:

The sample page is trivial.  It contains very little other than the Image Pull JavaScript.  Once we have completed basic testing, this page can be modified using an HTML page editor to contain the text and images of your own web page layout.

It is very tempting to modify the sample page at this point.  Don't do that for the initial tests.  It is easy to corrupt the page.  Once you have a basic page working, change the page incrementally to suit your own content.

The sample web page must be uploaded to your Webserver.  This requires that you have configured Webcam32 for basic FTP image upload.  This is described in detail:

Once basic still image FTP setup has been configured, the IP Upload capability of Webcam32 must be setup.  In the IP Upload tab of the FTP Settings dialog (see below), the following changes must be made:

Once these settings have been entered, press the Upload Now button to upload the page immediately.  The page will be re-uploaded every time we restart Webcam32.

When Webcam32 uploads the page, the HTML is modified before upload to include the current TCP/IP address of the machine running Webcam32.

Part 3 - Testing

At this point, we should have configured Webcam32 as described above.  We are now ready for testing.

Make sure that Webcam32 is running and shows a video preview.

Start a browser (either Netscape or Internet Explorer will be fine).  In the URL to surf to field at the top, enter the URL to your personal pages on the Webserver and the page imagepull.html.

For example, if your Webserver page is

http://www.myisp.net/~johndoe

enter

http://www.myisp.net/~johndoe/imagepull.html

The page should load and start displaying with live video images.

Additional Image Pull references