sudo apt-get install mplayerthumbs
Now, open Dolphin settings:
View modes>General>Previews>[x]Video files (mplayer thumbs)
You may need to add the following line to apt sources:
deb http://ubuntu.mirror.cambrium.nl/ubuntu/ precise main multiverse
Now update sources and then install again. If it still doesnt work, you can download a deb from here.
Joel G Mathew, known in tech circles by the pseudonym Droidzone, is an opensource and programming enthusiast.
His favorite pastime is grappling with GNU compilers, discovering newer Linux secrets, writing scripts, hacking roms, and programs (nothing illegal), reading, blogging. and testing out the latest gadgets.
When away from the tech world, Dr Joel G. Mathew is a practising ENT Surgeon, busy with surgeries and clinical practise.