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Posted 24 Oct 2006


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Streaming over HTTP with JavaScript: AJAX video player

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24 Oct 20068 min read
In this article, we simulate data streaming with JavaScript and talk about its potentials to perform the tasks associated with plug-ins.



Streaming is mostly referred as a delivery system for media content or dynamic data where it is beneficial to begin processing while data is being delivered. In reality, HTTP was not designed for data streaming. HTTP communications are stateless, and they take place over TCP/IP where there is no continuous connection between the ends. Usually, HTTP responses are buffered rather than streamed. HTTP 1.1 added support for streaming through keep-alive header so data could be streamed, but yet for performance proposes, the majority of implementations including ASP.NET tend to buffer the content, send it, and close the connection. As a result, there are few real world applications that use HTTP for streaming data, and normally, an additional protocol is built on top of HTTP for reconnection and error detection. However, this does not pose a problem because there are other UDP-based protocols that can be used for streaming where it is needed.

So, why would we need data streaming over HTTP? Because, we build our web applications over HTTP. Playing video clips, displaying RSS fields, and updating time sensitive data are considered common features of a webpage nowadays, but yet, we are bounded to HTTP capabilities. Here is where the browsers make use of plug-ins to overcome these boundaries, and also add new troubles!

Plug-ins are executed outside of your application’s context. Unlike Hyper Text Markup Language or JavaScript, plug-ins are mainly compiled binaries and they are difficult to customize. This is not to mention security, accessibility, platform independency, and web standards issues that are involved in pages that use plug-ins. While using plug-ins seems to be inevitable for pages with rich contents, AJAX has created high hopes in my opinion. Even though JavaScript language, as the version of today (the latest 1.7 in Firefox 2), is not fully capable of performing the tasks associated with plug-ins, I believe the future versions can offer enough browser integration and supporting libraries which eliminate the need of using complied plug-ins. I know this sounds very abstract, that is why I decided to write an AJAX application that does the most common task associated with plug-ins: video player. This AJAX video player is a scripted prototype-based video player that runs in JavaScript enabled HTML browsers that support Base64 encoded images (almost all modern browsers but IE). The AJAX video player can broadcast live (using an XML service) or cached video streams (XML file) to a variety of users on different platforms and browsers.

Live sample: Watch the Snoopi at pumpkin patch from AJAX Video Player!

Using the code


A video is a sequence of framed images that are displayed at a rate one after another. If we had all frames of a video clip in our browser, we could display them one after another at a frame rate and there we had our video playing! This sounds like a plan, let us see how we can translate this into an actual web application. From what we planned, we divide our efforts into smaller steps:

Step 1: Getting the frames, frame rate and other necessary information from a video file or a live stream

Step 2: Transport our frames over HTTP to the client’s browser.

Step 3: Animate the frames at the client, response to user interaction and request for more frames if needed.

Step 1: Getting the frames, frame rate and other attributes of video clip

If you have experience with writing applications in Microsoft DirectShow Editing Services (codename Dexter), this will sound very familiar to you. In the Windows environment, traditionally capturing still frames has been done using C++ and Dexter Type Library to access DirectShow COM objects. To do this in .NET Framework, you can make an Interop assembly of DexterLib which is listed under COM References in VS 2005. However it takes you a good amount of work to figure out how to convert your code from C++ to C# .NET. The problem occurs when you need to pass in a pointer reference as an argument to a native function, CLR does not directly support pointers as the memory position can change after each garbage collection cycle. You can find many articles on how to use DirectShow on the CodeProject or other places and we try to keep it simple. Here our goal is to convert a video file into an array of Bitmaps and I tried to keep this as short as possible, of course you can write your own code to get the Bitmaps out of a live stream and buffer them shortly before you send them.

Basically we have two option for using the DirectShow for converting our video file to frames in .NET:

  • Edit the Interop assembly and change the type references from pointer to C# .NET types.
  • Use pointers with unsafe keyword.

We chose the unsafe (read fast) method. It means that we extract our frames outside of .NET managed scope. It is important to mention that managed does not always mean better and unsafe does not really mean unsafe!

MediaDetClass mediaClass = new MediaDetClass(); 
_AMMediaType mediaType; 
... //load the video file
int outputStreams = mediaClass.OutputStreams;
for (int i = 0; i < outputStreams; i++) 
  mediaClass.CurrentStream = i; 
     //If it can the get the framerate, it's enough,
     //we accept the video file otherwise it throws an exception here
     outFrameRate = mediaClass.FrameRate; 
     //get the attributes here
    { // Not a valid meddia type? go to the next outputstream } 
// No frame rate? 
if (outFrameRate==0.0)
    throw new NotSupportedException( " The program is unable" + 
                                     " to read the video file."); 
// we have a framerate? move on... 
//Create an array to hold Bitmaps and intilize 
//other objects to store information...

unsafe { 
    // create a byte pointer to store the BitmapBits   
   while (currentStreamPos < endPosition) 
      mediaClass.GetBitmapBits(currentStreamPos, ref bufferSize, 
                               ref *ptrRefFramesBuffer, 
                               outClipSize.Width, outClipSize.Height); 
   //add frame Bitmap to the frameArray

Step 2: Transfer extracted data over HTTP

So far we have converted our video to an array of Bitmap frames. The next step is to transfer our frames over HTTP all the way to the client’s browser. It would be nice if we could just send our Bitmap bits down to the client but we cannot. HTTP is designed to transport text characters which mean your browser only reads characters that are defined in the HTML page character set. Anything else out of this encoding cannot be directly displayed. 

To accomplish this step, we use Base64 encoding to convert our Bitmap to ASCII characters. Traditionally, Base64 encoding has been used to embed objects in emails. Almost all modern browsers including Gecko browsers, Opera, Safari, and KDE (not IE!) support data: URI scheme standard to display Base64 encoded images. Great! Now, we have our frames ready to be transferred over HTTP.

System.IO.MemoryStream memory = new System.IO.MemoryStream();
while (currentStreamPos < endPosition) 
  // Save the Bitmpas somewhere in the (managed) memory 
  vdeoBitmaps.Save(memory, System.Drawing.Imaging.ImageFormat.Jpeg); 
  //Convert it to Base64
  strFrameArray[frameCount] = System.Convert.ToBase64String(memory.ToArray()); 
 //Get ready for the next one
  memory.Seek(0, System.IO.SeekOrigin.Begin); 

But we cannot just send out the encoded frames as a giant string. We create an XML document that holds our frames and other information about the video and then send it to the client. This way the browser can receive our frames as a DOM XML object and easily navigate through them. Just imagine how easy it is to edit a video that is stored in XML format:

<?xml version="1.0" encoding="utf-8"?>
  <Clip name="Snoopi">
        <Clip_Size>{Width=160, Height=120}</Clip_Size>
     <Frame ID="96">/9j/4AAQSkZJRgABAQEAYAB.... </Frame>

This format also has its own drawbacks. The videos that are converted to Base64 encoded XML files are somewhere between 10% (mostly AVI files) to 300 % or more (some WMV files) bigger than their binary equivalent.

Figure 1 shows the data flow in our AJAX Video Player application.

Figure 1: Data flow in AJAX Video Player

Image 1

If you are using an XML file, you even don't need a web server , you can open the HTML from a local directory and it should work! I included an executable in the article's download file that can convert your video file to XML document which later can be shown in the browser. However using big files and high resolution videos is not a good idea!

OK, now we can send out our “Base64 encoded video” XML document as we would do with any other type of XML files. Who says XML files always have to be boring record sets anyway?!

Step 3: Animate the frames at the client

Figure 2 shows the application flow in the JavaScript VideoPlayer object. I tried to comment the code as much as possible. You can view the source code in the download provided with this article.

Figure 2: Application flow in AJAX Video Player

Image 2


In this article, we simulated data streaming with JavaScript and  talked about its great potentials to perform the tasks associated with plugins, although it will be a while until it can replace them in real world applications.  A more featured JavaScript with better OOP support is beneficial to everybody. When it comes to developing JavaScript features many conservative precautions have been considered just to open the door for all sort of plug-ins! Java to JavaScript compliers have already started to squeeze as much as possible out of JavaScript. Google (GWT) and Mozilla (here) have released great compliers to convert your Java code to JavaScript.

Some time in the future :) in another article we talk about how JavaScript can improve the MVC design pattern of a web application by loosely coupling viewers (HTML pages) and controllers (classes in an XML Service). In some scenarios JavaScript can completely replace your web controls and save you from going through ASPX page life cycle.

Appendix - Related Links


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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Comments and Discussions

BugI get an error when I press the play button Pin
gordingin25-Jul-14 2:52
Membergordingin25-Jul-14 2:52 
Questionframes to video output file? Pin
surbob15-Feb-13 19:47
Membersurbob15-Feb-13 19:47 
QuestionDoubt in video data Pin
Muthukumar002313-Dec-11 16:56
MemberMuthukumar002313-Dec-11 16:56 
GeneralVideo Streaming Pin
Prerna Sancheti27-Feb-11 8:52
MemberPrerna Sancheti27-Feb-11 8:52 
QuestionWhat is author's mail id ?? Pin
narendra.sisodiya23-Aug-08 11:03
Membernarendra.sisodiya23-Aug-08 11:03 
AnswerRe: What is author's mail id ?? Pin
soulsouw18-May-12 10:13
Membersoulsouw18-May-12 10:13 
Questionvedio streaming Pin
amoon1081-Apr-08 10:49
Memberamoon1081-Apr-08 10:49 
Questionseeking help on video streaming Pin
punk grunge19-Dec-07 0:01
Memberpunk grunge19-Dec-07 0:01 
Questionall about setting server for this app Pin
rikkududut30-Nov-07 0:18
Memberrikkududut30-Nov-07 0:18 
Generalgood work Pin
AchalShah24-Jan-07 0:48
MemberAchalShah24-Jan-07 0:48 
QuestionEnhancement for IE? Pin
Liang Yu8-Dec-06 17:38
MemberLiang Yu8-Dec-06 17:38 
AnswerRe: Enhancement for IE? Pin
Diabolus Hell26-Apr-07 22:19
MemberDiabolus Hell26-Apr-07 22:19 
Questionhow bout divide the xml? Pin
rikkududut29-Nov-06 21:05
Memberrikkududut29-Nov-06 21:05 
AnswerRe: how bout divide the xml? Pin
Shahin__29-Nov-06 21:34
MemberShahin__29-Nov-06 21:34 
QuestionCapturing sound Pin
Adnan Siddiqi21-Nov-06 23:14
MemberAdnan Siddiqi21-Nov-06 23:14 
AnswerRe: Capturing sound Pin
Shahin__22-Nov-06 15:11
MemberShahin__22-Nov-06 15:11 
GeneralRe: Capturing sound Pin
Adnan Siddiqi22-Nov-06 19:40
MemberAdnan Siddiqi22-Nov-06 19:40 
QuestionCaching Pin
Adnan Siddiqi19-Nov-06 18:50
MemberAdnan Siddiqi19-Nov-06 18:50 
AnswerRe: Caching Pin
Shahin__19-Nov-06 21:39
MemberShahin__19-Nov-06 21:39 
Questioncomparison with flash and xMPP etc Pin
Adnan Siddiqi20-Nov-06 9:07
MemberAdnan Siddiqi20-Nov-06 9:07 
Questionwhat method you used here? Pin
rikkududut17-Nov-06 2:43
Memberrikkududut17-Nov-06 2:43 
AnswerRe: what method you used here? Pin
Shahin__19-Nov-06 21:31
MemberShahin__19-Nov-06 21:31 
GeneralRe: what method you used here? Pin
rikkududut23-Nov-06 14:15
Memberrikkududut23-Nov-06 14:15 
AnswerRe: what method you used here? Pin
Shahin__27-Nov-06 17:28
MemberShahin__27-Nov-06 17:28 
GeneralRe: what method you used here? Pin
rikkududut28-Nov-06 17:43
Memberrikkududut28-Nov-06 17:43 

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