Setting to make .mp3 files autoplay in Viewer

On one of my computers (not with me at the moment) when I click on an .mp3 file it will autoplay the audio file in the Viewer pane. Which setting do I have to enable to make it do that? Or is that something from within Windows Media Player?

Here is how it shows for me now (not autoplaying; I have to click play.)

The WMP Preview Handler will never auto-play, while the WMP ActiveX control can auto-play.

You can configure which is used for different extensions via Preferences / Viewer / Plugins and then configuring the ActiveX + Preview + Office + Web plugin. (You've probably seen it before as the WMP Preview Handler is turned off by default unless you change it int he same place.)