From Apple Support Article HT205081 available here.

If your web browser says that it‘s missing the QuickTime plug-in

A small number of older webpages still rely on the legacy QuickTime 7 web plug-in to play media. This plug-in is no longer enabled in recent versions of OS X and some web browsers.

If you visit a webpage that requires the legacy QuickTime 7 web plug-in, your web browser might display a message that the plug-in is missing or not supported.
This plug-in is no longer enabled in OS X El Capitan, Yosemite, and Mavericks. Websites increasingly use the HTML5 web standard for a better video-playback experience across a wide range of browsers and devices.
Recent versions of some third-party web browsers no longer support legacy web plug-ins.
Restore the plug-in, if necessary

If you can't wait for the author to update their webpage, you can restore the legacy QuickTime 7 web plug-in. Leaving legacy browser plug-ins disabled enhances the security of your Mac, so you should take these steps only if necessary.
Make sure that you're using Safari or another browser that supports legacy web plug-ins.

1. Choose Go > Go to Folder from the menu bar in the Finder.

2. Type /Library/Internet Plug-Ins in the search field, then click Go. The Internet Plug-Ins folder opens.

3. While holding down the Command (⌘) key, double-click the Disabled Plug-Ins folder to open it in a new window.

4. Drag these two files from the Disabled Plug-Ins folder to the Internet Plug-Ins folder:
QuickTime Plugin.plugin
nslQTScriptablePlugin.xpt
If you're asked to authenticate, click Authenticate, then enter an administrator name and password.

5. Quit your web browser, then open your browser again. You should now be able to play the media.

To disable the legacy QuickTime 7 web-plug-in again, move both files back to the Disabled Plug-Ins folder.