I have already talked about SignalR in this blog. I think it is one of the most interesting technologies that Microsoft put out recently, not because it is something substantially new – AJAX, long polling and server-sent events have been around for quite some time -, but because of how easy and extensible they made it.
Most of the examples of SignalR usually are about chat. You know that I have been digging into HTML5 lately, and I already posted on media acquisition using HTML5’s getUserMedia API. This time, however, I’m going to talk about video streaming!
I wrote a simple ASP.NET Web Forms control that leverages SignalR to build a real-time communication channel, and this channel transmits images as Data URIs. The source of the feed comes from getUserMedia and is therefore available in all modern browsers, except, alas, one that shall remain unnamed. Any browser, however, can be used to display the streaming feed.
So, the architecture is quite simple:
One SignalR Hub for the communication channel;
One ASP.NET Web Forms control, that renders an HTML5 VIDEO tag that is used to display the video being acquired, on any compatible browser.
Here are some nice screenshots of my now famous home wall, where one of the browser instances, Chrome, is broadcasting to Firefox, Opera and Safari. Unfortunately, IE is not supported.
So, all we need is a control declaration on an ASP.NET Web Forms page, which could look like this:
The non-ordinary properties that the VideoStreaming control supports are:
Interval: the rate in milliseconds that the control broadcasts that the video is being broadcast; do not set it to less than 200, from my experience, it will not work well;
Source: if the control is set as a streaming source, or just as a receiver (default);
And a simple CANVAS element for Target:
The reason for the two main streaming modes, Target and Event are flexibility: with Target, you directly draw the streamed picture on a CANVAS or IMG (it will detect automatically what to use), which needs to be already present, and with Event, you can do your own custom processing.
The source for the VideoStreaming control is this:
Renders a VIDEO tag element with the specified Width and Height;
Register a SignalR hub;
Removes any eventual VIDEO-related attribute that may be present on the control declaration;
Of course, we now need the hub code, which is as simple as it could be, just a method that takes the image as a Data URI and its original dimensions and broadcasts it to the world:
And finally the simple enumerations used by the VideoStreaming control:
And there you have it! Just drop the VideoStreaming control on an ASPX page and you’re done! If you want to have it broadcast, you need to set its Source property to true, for example, on the containing page:
That’s it. Very simple video streaming without the need for any plugin or server. Hope you enjoy it!