Well this is the cause of your problem then:
I use the library in a NAS with SMB protocol
iPhoto needs to have the Library sitting on disk formatted Mac OS Extended (Journaled). Users with the Library sitting on disks otherwise formatted regularly report issues including, but not limited to, importing, saving edits and sharing the photos.
So this problem - and others - will pop up with increasing regularity as time goes on.
So, move the Library to an appropriately formatted disk. See if the videos will import then. If not then
Back Up and try rebuild the library: hold down the command and option (or alt) keys while launching iPhoto. Use the resulting dialogue to rebuild. Choose to Repair Database. If that doesn't help, then try again, this time using Rebuild Database.
If that fails:
Download iPhoto Library Manager and use its rebuild function. (In Library Manager it's the FIle -> Rebuild command)
This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.
Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one.
I too am having the same problem importing videos from an iPhone 5 into my iPhoto library. Photos import fine.
I set the iPhoto library up as new following the instructions by Apple for setting up a shared iPhoto library here:
As far as I can tell, based on the existance of this article, Apple do support shared iPhoto libraries, as long as the permissions are set up right, which I've done.
I still can't import vidoes though, and this is a new iTunes library created on the mounted drive shared over a local network.
I took the disk image approach. I created a read/write disk image in a shared location, set up a new iPhoto library on it and set the drive to 'ignore permissions' and the library file itself to 'everyone can read/write', then shared the volume on the network and mounted it on my laptop which is where I have the iPhone plugged in.
It all works fine, including importing photos, just not vidoes.
I have some considerations to this issue. I had tried to use iPhoto over a NAS storage using SAMBA (Windows Shares) and always have some issues even with the sparse images. I was only sucessfull using iPhoto over NFS and even with that some times when I got a NFS disconection I had too a library corruption, using an ISCSI storage got me far but after two or three times corruption library I have give up iPhoto and returned to Picasa.
Anyway, even with a sparce disk image is better to go to NFS or ISCSI shares or you will constantly miss some funcions on library.
Holpe this helps.