One of the features I really love in OS X is the ability to preview anything by selecting the file in finder and pressing the spacebar – formally called ‘Quick Look’ – without actually having to open the full app. This is great for both music and movies.
However, if you uninstalled Perian or Flip4Mac or haven’t updated them recently, you will find that a lot of movie files – like .avi, for example – which are not fully supported in QuickTime won’t preview. The answer is to get the latest versions of these two plug-ins:
(hit the green download button (free), ignore the one trying to sell you a paid version).
You should then be able to see any movie using Quick Look.
QuickTime won’t play my video