You might have noticed that some of your videos no longer have a Finder preview in Mavericks. Macworld’s Chris Breen discovered that Apple has deprecated many of its older codecs in favor of the iOS-compatible H.264 and MPEG-4. To watch older video files, you must convert them with QuickTime X, install Apple’s professional codecs (if you bought Final Cut Pro, Motion, or Compressor), or use a more capable app like QuickTime 7 Pro or MPlayerX. follow link
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Why Your Videos Won’t Preview in OS X 10.9 Mavericks