If you have a large collection of videos and want an easy way to preview them, try putting them in a folder and setting the folder to icon view. Then choose View, Show View Options and set the icon size to 64×64 or higher. Now you get a play button at the center of each icon and can play the video inside the icon. You can also do this in Cover Flow view, which gives you a list at the bottom and playable cover flow icons at the top.
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