Skip to main content

Pushing HTML5 Video content over ColdFusion WebSockets

I’ve been playing with the WebSocket feature introduced in ColdFusion 10 for some time now. I was trying out pushing images over a ColdFusion WebSocket channel and it worked just fine. But this time I wanted to put WebSockets to test and wanted to push large data at regular intervals. I thought maybe I can push video data over WebSockets and it turned out that there is no direct way to stream video data to many clients. I came across the function - drawImage that can be used to draw an Image or Video on a HTML5 Canvas. Once an image is drawn on the Canvas, it’s base64 encoded data can be obtained by calling the toDataURL function on the Canvas object.  This data can then be transferred over a ColdFusion WebSocket to all subscribers who can then use this  data to draw the image(video frame) on a Canvas.

Here’s the demo video:

Unable to display content. Adobe Flash is required.

If you are not able to view the above video, please visit http://screencast.com/t/C8tyv1TejJpp. Please note, I’m not transferring the audio track present in the Video and I’m still trying to figure how that can be achieved.

Here’s the Publisher code:

<!DOCTYPE html> <html> <body> <cfwebsocket name="socket" onmessage="messageHandler"> <video id="videoElement" controls muted> <source src="windowsill.webm" type="video/webm"> </video> <br> <canvas id="canvasElement" style="border: solid 1px;"> </canvas> <script type="text/javascript"> var context,canvasElement,videoElement, previous, current; //message handler for CF WebSocket messageHandler = function(msg){ } //function to call once the DOM content has been loaded document.addEventListener('DOMContentLoaded', function(){ videoElement = document.getElementById('videoElement'); canvasElement = document.getElementById('canvasElement'); context = canvasElement.getContext('2d'); }); //function to call once the videos meta data is available document.getElementById('videoElement').addEventListener('loadedmetadata', function(){ //set the canvas width and height to videos width and height canvasElement.width = videoElement.videoWidth; canvasElement.height = videoElement.videoHeight; //event listener when the video is played videoElement.addEventListener('play', function(){ //call the draw function draw(this, videoElement.videoWidth, videoElement.videoHeight); }); }); //function to draw the video frame on a temporary canvas at 20fps function draw(video, width, height){ //if the video has been paused or ended return false if (video.paused || video.ended) return false; //draw the current video frame onto a canvas context.drawImage(video, 0, 0, width, height); //get base64 encoded data from Canvas current = canvasElement.toDataURL("image/png"); //just in case if the previous frame is same as current if (previous != current) { //transfer the base64 encode image over a WebSocket socket.publish("myChannel", current); } previous = current; //draw the video frame on the canvas at 20fps by calling the draw function every 50ms setTimeout(draw, 50, video, width, height); } </script> </body> </html>

As you can see from the above code, once you start playing the video the draw function is called. Here I've drawn the video on a Canvas using the drawImage function and then used the function toDataURL to get the base64 encoded data of the image. This is then transferred over a ColdFusion WebSocket channel (‘myChannel’). I’m calling this function (‘draw’) every 50ms to draw the current video frame on the canvas (to achieve 20fps) and transfer the image over a WebSocket.

The client\subscriber on receiving the data, draws  the image (video frame) on a canvas. Here’s the subscriber code:

<!DOCTYPE HTML> <html> <body> <cfwebsocket name="socket" onmessage="messageHandler" onopen="openHandler"> <canvas id="canvasElement" style="border: solid 1px;" width="426" height="240"> </canvas> </body> <script type="text/javascript"> var canvas, context, count = 0, flag = false; var newImage = new Image(); document.addEventListener('DOMContentLoaded', function(){ canvas = document.getElementById('canvasElement'); context = canvas.getContext('2d'); }); function openHandler(){ //subscribe to the CF WebSocket channel socket.subscribe("myChannel", {}, dataHandler); } function messageHandler(msg){ } //function that receives the data from the WebSocket channel function dataHandler(msg){ if (msg.type == 'data') { //function to call when the image is loaded with base64 data newImage.onload = function(){ //draw the image on the canvas context.drawImage(newImage, 0, 0); //set the flags when the above function is complete flag = true; count = 1; } //if ready to be drawn on the canvas if (count == 0 || flag == true) { flag = false; //assign base64 data to the source of the image newImage.src = msg.data; } } } </script> </html>

On the client side, once the data is received over the WebSocket it is assigned to the source of an Image object. The reason why I do this is because the drawImage function takes either an Image or a Video as it's first argument and doesn't allow base64 data. Once the Image is loaded, it is ready to be drawn on the canvas. This process continues until the video ends or the user pauses the video.

Comments

Popular posts from this blog

Custom validation messages for HTML5 Input elements using the constraint validation API

HTML5 has introduced several input types such as EMAIL, URL, RANGE, SEARCH, DATE, TIME, etc,. Most of the modern browsers have implemented them and are ready to be used in a HTML document. Another exciting feature introduced in HTML5 is the form validation. Instead of writing JavaScript to validate users input, browsers can now validate it and show an appropriate message if the validation fails. The validation message is shown in line with the field for which the validation has failed. The default error message is shown when the validation fails. In this post I'll explain how these error messages can be changed.

Adding beforeRender and afterRender functions to a Backbone View

I was working on a Backbone application that updated the DOM when a response was received from the server. In a Backbone View, the initialize method would perform some operations and then call the render method to update the view. This worked fine, however there was scenario where in I wanted to perform some tasks before and after rendering the view. This can be considered as firing an event before and after the function had completed its execution. I found a very simple way to do this with Underscore's wrap method.

A cheat sheet of keyboard shortcuts in ColdFusion Builder

In my last post I have explained about keyboard shortcuts in ColdFusion Builder 2.0. This blog post contains a list of all shortcut keys and I have listed these keyboard shortcuts based on the categories that it falls into. Well, this post was not planned since users can easily get to know the keyboard shortcuts by navigating to the preferences (ColdFusion -> Profiles -> Keys). However, I met Joshua at Scotch on the rocks in Edinburgh and he suggested that it would be nice to have the list of keyboard shortcuts handy. So this post is for those who would like to have the list with them and refer it whenever required.


Keyboard shortcuts for inserting text:

These are the keyboard shortcuts which are used to insert some text into the editor:

CommandKeyboard shortcuts on WindowsKeyboard shortcuts on MacInsert anchor tagCTRL + T, LCMD + T, LInsert bold tagCTRL + T, BCMD + T, BInsert br tagCTRL + T, RCMD + T, RInsert cfabortCTRL + T, ACMD + T, AInsert cfdumpCTRL + T, DCMD + T, DInsert cfs…