A Closer Look at the Microsoft h.264 Extension for Chrome
February 3, 2011 Leave a comment
Today I took a closer look at how the “Windows Media Player HTML5 Extension for Chrome” works. To recap for a moment, Google announced that they are revoking native h.264 playback for the HTML5 <video/> tag in Chrome. A huge kerfuffle ensued. Yesterday, Microsoft announced that they were providing an extension to Chrome that provides h.264 support for the <video/> tag in Chrome on Windows 7.
I downloaded the CRX file and unzipped it. This is the contents:
PS> ls | select Length, Name | ft -AutoSize Length Name ------ ---- 6540 contentscript.js 678 manifest.json 163256 np-mswmp.dll 59413 wmp eula.rtf 3489 wmp releasenotes.txt 28177 wmp128.png 569 wmp16.png 2233 wmp48.png
The np-mswmp.dll file looked familiar. And that is because it is the NSAPI plugin for Windows Media Player for Firefox.
The remaining interesting file in the CRX is contentscript.js. In a nutshell, what this script does is look for <video/> elements that are referencing h.264 or WMV content and dynamically replace them with <object type=”application/x-ms-wmp” /> element referencing the same content.
The Windows Media NSAPI plugin is installed into Chrome along with this extension which means any pages which explicitly embed the Windows Media Player will work.
Also, this extension enables support for WindowsMedia Video content in <video/> elements.
var supportedMimeTypes = ['video/mp4', 'video/x-ms-wmv']; var supportedVideoExtensions = ['.mp4', '.wmv', '.mp4v', '.m4v'];
Windows 7 Not Really Required
The Windows Media NSAPI plugin was released by the Port 25 group at Microsoft in April 2007. It doesn’t rely upon Windows 7 to work. The issue is just that Windows 7 is the first version of windows to ship with an h.264 codec for Windows Media Player. The extension should work on Windows XP and Vista if you have an h.264 codec for Windows Media, such as from the K-Lite codec pack.
Pointing the Way for Alternate Cross-Platform Implementations
This general approach also points the way for a 3rd party that has an NSAPI plugin that supports h.264 to extend Chrome (and Firefox) to support h.264 and whatever else the video player can support in the <video/> element. In particular it should be straightforward to create an extension that uses the VLC NSAPI plugin to extend the <video/> tag codec to support h.264 as well as DivX, QuickTime and MPEG-2.