audio and video stutter

I appear to be experiencing some weird video and audio stutters on my iPhone 4S under iOS V5.1.1.

I started watching a Video of Game of Thrones Series 2, which appeared to play the same scene twice.

I have checked the video source that I encoded from to check there were no anomalies in the video itself.

Then when I played music from the device I noticed stuttering on audio I know is clean and has no problems.

Has anyone else expeienced such a problem please?

I have rebooted the device but the issues appears to return after a while.

thanks in advance

G