Video freezing when playing mkv file over Airplay and ftp server


I have a problem when playing mkv files over airplay with my iphone 6.
When I play a mkv movie on the device, everything is ok, works fine (let me precise that my files are located on a home server)
But, when I activate airply function, the video plays for a couple of seconds, then freezes ans plays again for another couple of seconds, then freezes again and so on…

Can anyone help me with that ?

I have disabled Dolby in airplay and audio efects Dolby.

(sorry for my English ;))