problems with mkv playback on pms

Hi everybody
I use plex media server on my mac and everything works fine except for some new mkv files...

I explain it... If i use the italian language the video continuosly go jerkily (go in spurts... Sorry for the bad translattion)...

These are the specifics of the file..

Thank you for tour cooperation!!



Media
Video Resolution 1080p
Durata 48:52
Bitrate 4494 kbps
Width 1920
Height 960
Aspect Ratio 1.85
Container MKV
Video Frame Rate PAL
Parte
Durata 48:52
File xxxxxxxxxxxxxxITA-ENG.1080p.BDMux.DD5.1.x264-NovaRip.mkv
Size 1.53 GB
Container MKV
Video
Codec H264
Bitrate 3636 kbps
Lingua English
Bit Depth 8
CABAC 1
Chroma Subsampling 4:2:0
Color Space yuv
Durata 48:52
Frame Rate 25.000 fps
Frame Rate Mode cfr
Has Scaling Matrix 0
Height 960
Level 4.1
Profile high
Ref Frames 4
Scan Type progressive
Width 1920
Audio
Codec AC3
Canali 5.1
Bitrate 384 kbps
Lingua Italiano
Bit Depth 16
Bitrate Mode CBR
Dialog Norm -24 dB
Durata 48:52
Sampling Rate 48000 Hz
Audio
Codec AC3
Canali 5.1
Bitrate 384 kbps
Lingua English
Bit Depth 16
Bitrate Mode CBR
Dialog Norm -31 dB
Durata 48:52
Sampling Rate 48000 Hz
Sottotitoli
Forzato 1
Codec SRT
Format SRT
Sottotitoli
Codec SRT
Lingua Italiano
Format SRT
Sottotitoli
Codec SRT
Lingua English
Format SRT