Sony KDL32V5500 (2009) transcoding issues

Hi
Firstly - Serviio is great - far better than my fall back option of Windows Media Center!
However, I have a problem with certain file types that work marginally better in WMC.
DVR-MS - when I try to view these files, the video is barely watch-able, being very 'jerky' and slightly pixelated. Gives the impression the PC is struggling to transcode at a suitable rate, but I don't think CPU is the issue.
MP4 - these files just send the TV crazy. Sometimes it's like they are on permanent fast forward and on occasion I've had to switch the TV off to recover it!
Everything else works perfectly though. I can, for example transcode an HD quality file, eg an FLV or MPG without issue.
Any ideas - I'm pretty new to this but if you let me know what to do/post I will - really appreciate any help you can give!
Thanks
Firstly - Serviio is great - far better than my fall back option of Windows Media Center!
However, I have a problem with certain file types that work marginally better in WMC.
DVR-MS - when I try to view these files, the video is barely watch-able, being very 'jerky' and slightly pixelated. Gives the impression the PC is struggling to transcode at a suitable rate, but I don't think CPU is the issue.
MP4 - these files just send the TV crazy. Sometimes it's like they are on permanent fast forward and on occasion I've had to switch the TV off to recover it!
Everything else works perfectly though. I can, for example transcode an HD quality file, eg an FLV or MPG without issue.
Any ideas - I'm pretty new to this but if you let me know what to do/post I will - really appreciate any help you can give!
Thanks