[PROBLEM] Playback speed of 1080p dts movie is slowing down

[Smieh]

hi there,

got a little problem here with my pi + xbian.

Software
XBian version: 1.0 beta 2
XBMC version: 12.2 (the standard version that comes with beta 2)
Overclock settings: default

Hardware
Power supply rating: 2A
RPi model (model A/B 256mb/512mb): B / 512
SD card size and make/type: SanDisk 8GB microSDHC
Network (wireless or LAN): LAN (100MBit)
Connected devices (TV, USB, network storage, etc.): Audio Receiver via HDMI (DTS / DTSHD capable), LAN

Problem description:
Got the following 2 files:


Both files are located on the same NAS connected to xbian via SMB.

The first one (located on top) plays fine without any problems.
The second one plays well for the first 2-3 minutes but after that time - something strange happens. It seems like xbmc is reducing the playback speed of the movie - it runs without any drops or stuttering but only at about half the speed (if you don't know what i mean - open a video file in vlc on your desktop an reduce the playback speed to 0.5x).

The only difference i see is the different overall bitrate (11 vs. 23 Mbps) - had the same problems with another file which was also equal to the 2 files from the screenshot but had an overall bitrate of 16 Mbps. If i convert DTS to AC3 5.1 the 23Mbps and the 16Mbps file work fine.

Any ideas?
Is there a possibility to check the connection speed between my nas and the pi? (i assume that maybe the 23Mbps is just too much data although that shouldn't be a problem for a 100MBit network...)