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
A problem that seems to be affecting quite a few users after the Mountain Lion upgrade is loss of sound in iTunes, QuickTime and other apps. Some people are reporting that the Volume control is greyed out or won’t move.
The resolution here is to quit and resart the coreaudio process. To do so:
1. Open Activity Monitor.app (Applications > Utilities > Activity Monitor.app)
2. Select ‘All Processes’ from the drop down menu next to the search bar (called ‘Filter:’) and type in ‘coreaudio’.
3. Select the process name and click the ‘Quit Process’ button at the top. Chose ‘Quit’ or ‘Force Quit’ from the resulting dialogue box.
The coreaudio process will automatically restart itself (if you look closely at the PID number in Activity Monitor you’ll notice it changes after you hit ‘Quit’) and your sound problems should be solved. However, if you find that this procedure only partially solves the problem or doesn’t work for you, also try this:
4. Open Terminal.app (Applications/Utilities/Terminal.app) and copy/paste this command into the Terminal window
then press ‘return’ on your keyboard.
5. Restart your mac and test.
6. Still not working? Check your audio configuration here:
/Applications/Utilities/Audio MIDI Setup.app.
Make sure the window has the title Audio Devices, and click ‘Built in Output’ in the sidebar. Are any of the boxes under ‘Mute’ in the main panel checked? If so, uncheck them. Is the format set to 44100.0hz? If not, change it so that it is.
Hope this helps!