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
Go Back and Forth Fast in Preview
If you're reading a PDF in Apple's Preview software, and you follow a bookmark or an internal link to move around within the PDF, you can quickly return to where you were by pressing the keyboard shortcut Command-[ (that's Command-Left Bracket). Or, you can choose Go > Back.
The command works iteratively, so you can go back to just the previously viewed page or if you issue the command again, to the page before that, and so on. There's also an equivalent Go > Forward (Command-]).
- ExtraBITS for 4 November 2013 (04 Nov 13)
Why Your Videos Won’t Preview in OS X 10.9 Mavericks