I was very excited when Microsoft released the Internet Explorer 9 Release Candidate. As far as I was concerned, this was another nail in the coffin for IE6 and step in the right direction for us .NET web developers as our base camp was finally starting to support the latest and greatest future-web standards.

Unfortunately, my celebration was short lived as I soon hit a snag while loading up an HTML5 site I was building in Visual Studio 2010.

The Mystery

After updating Internet Explorer, I ran my HTML5 site that had the oh-so-lovely HTML5 video tag showing a video. Even though this worked in IE9 Beta, it appeared that IE9 RC could not load the same file. I figured that it was the video codec. Maybe IE9 RC no longer supported the video codec I used to encode my video. Here's the code I used:

<video width="854" height="480" id="myOtherVideo" autoplay="" controls="">
    <source src="/DemoSite1/Media/big_buck_bunny.mp4"/>
    <div>
        <p>Your browser does not support HTML5 Video.</p>
    </div>
</video>

As you can see from the code, I had the "fail-safe" code inside the video tag. The idea there being that if the video tag, or the video files themselves, are not supported by the browser my video should fail gracefully.

What was even more strange was the fact that it worked in all the other HTML5 browsers that supported video.

The Investigation

Whoa! DJ stop the music. How can any of that make sense? Would the IE team really take such huge strides forward only to forget to include a feature that was already in the beta? I don't think so.

I did plenty of searching on the web and asking around on the web, but could not seem to find anyone else having the same problem. Eventually I came across this post talking about declaring the MIME type in the .htaccess file.

That got me thinking: does my web server support the video MIME type? I was using VS2010, so how do I know what kind of MIME types are supported by default?

Still, my page hosted in Cassini (the web development server in VS2010) works on the other browsers. Why wouldn't it work with IE9 RC? To answer that, it was time to open up the upgraded toolbox known as the Developer's Tools in IE9 and use the new Network Tab.

The Conclusion

If you take a closer look at the results displayed from the Network tab, you can see that IE9 RC has interpreted the video file as text/html rather than video/mp4.

To make this work, I decided to use IIS to debug my HTML5 web application by setting the web project's properties. Then, I added the MIME types that I want to support (i.e. video/mp4, video/ogg, video/webm). Et voila! The Mystery of the Broken Video Tag is solved.

After Thoughts

After solving the mystery, I still had the question about why my site worked in Chrome, Safari, and Firefox 3.6. After asking around, the best answer that I received was from my colleague Tyler Doerksen. He said that IE9 likely depends on the server telling it what kind of file it is downloading rather than trying to read the metadata about the data it is trying to download before doing anything.

I have no facts to back this up, but it makes sense to me. In a browser war where milliseconds can make your browser fall back a few places in the race for supremacy, maybe the IE team opted to depend on the server knowing what kind of content it is serving up. Makes sense to me.

In any case, that is just an educated guess. If you have any comments, feel free to post on them below.

This post also appears at http://david.wes.st