I have exactly the same issue. Use Ubuntu 14.04 for the server. Tried it with SMB and NFS and it is exactly the same behaviour as you describe. Changing advancedsettings.xml have minimal effects if none. Playing the movie on another PC works flawlessly even over wifi.
What about if you copy the file to the pi and play from there?
there is only a switch between the pc and the rpi the same switch that is between the pc that plays it back fine, if copying the file to the pi and playing it back is the same as playing it back from USB i can tell you that that worked fine 
I’ll try once more with the SMB.
Ok I got my SMB share to work again, and tried playing back a movie, it stuttered a little bit in the beginning then played back fine for about 10 minutes then it stuttered some more and played back fine for another 10 minutes after this it started stuttering every minute. One thing i would like to add is the multicolored square in the top right corner also stays there.
color thingy = bad or under powered
Your power supply is too low or broken
jup found that out online allready ordered a new one, and hoping that will fix it.
I received my power supply today and the colored square is gone now so that’s good, but it’s still buffering.
Your router has USB and samba share?
Perhaps a laptop?
Trying to exclude the PC as possible problem.
The pc is not the problem it plays back fine on other pc’s.
bump
Even though the PC plays the files, its network adapter could have negative influence on the overall network.
Try again after disconnecting everything except the raspberry and router/nas.
If you’re using HD content, you will need to purchase the MPG2 or VC1 codec licenses (or both)-not all content is encoded in h.264 which licensing for is included with the Pi. I just set mine up last night and streaming content was pretty wonky. I ordered the codec licenses and got them in a few hours, from the Raspberry Pi store. That cleared up the stuttering problem beautifully.
I’m also using a SanDisk Extreme Plus MicroSD card-which is probably overkill-but you should use a card that is rated Class-10 with UHS-I as a minimum to avoid problems (it is a little more pricey, but it guarantees minimum performance better than the Class 10 rating alone). Kingston MicroSD cards are often very poorly reviewed for performance and reliability. It will also likely die faster than a more expensive card since it is doubtful it has any form of wear leveling (this is a feature where the controller in the memory card avoids writing to the same place on the card all the time) As a minimum you should also probably stick to cards with 16GB or more to ensure adequate storage for buffers, swap file, etc.
Sorry for the late answer i wasnt home with the new year and all, but i tried with only the nas and the rpi connected and it was still the same, and i’m trying 720p content.
Do ALL 720P files exhibit this? Provide mediainfo on a problematic file please.
Sorry again for the late answer have been really busy with school, it happens to ALL 720p files and above, lower i wouldnt know because the lowest i have is 720p. It is in h.264.
Did you try (a) different network cable(s)?
Sometimes crappy ones do not have the full 8 connections populated and only deliver 10MBit instead of 100.
Jup tried with 2 other cables exactly the same results.
bump
You probably aren’t getting much response here because your issue is almost certainly a speed/throughput issue on your local network. A bit outside the scope of this forum.
Yea probably but I wouldn’t know what the issue would be / how to go about fixing it, because when trying the transfer speed between the server and the raspberry pi, i get the speed i should get.
Also something different, I’m still using my osmc now with a USB stick and i had an update a while ago an everytime I try to install it it gives me a sadface.