I've tried running the qlmanage program from terminal with the -p (compute preview) option on one of the AVI files. Here is what is sent to the console output:
30/01/13 10:11:19.843 PM qlmanage: Failed to communicate with qtkitserver: Connection invalid
30/01/13 10:11:19.844 PM qlmanage: Failed to initializeServer(), returned 5
30/01/13 10:11:20.794 PM WindowServer: CGXDisableUpdate: UI updates were forcibly disabled by application "qlmanage" for over 1.00 seconds. Server has re-enabled them.
qtkitserver does not exist in the process list.
Maybe the initializeServr() function tries to activate it but fails - error code 5.
Does anyone know what these messages mean ?