Problem with BBC iplayer (Offline)

[FuzzyLogic]

Ive installed BBC iplayer on my Lenovo X220. The laptop itself has an SSD & happily plays HD offline content through VLC player.

If I download even SD content for BBC iplayer to use offline, the picture is consistently 'start / stop'. The video will start normally, freeze for a split second, then resume for a couple of seconds before freezing again. This repeats all the way through. Audio is not affected & when the video 'unfreezes' it remains synced to the audio..

I've re-installed iplayer, checked all the updates. windows (windows 7) is up to date and otherwise working fine...

Any ideas!? I've drawn a blank with Google before anyone asks!