OK thanks, you encouraged me to play around a little more. There's a
(well-buried) Preferences menu option that seems to show the
connection defaulting to 128kbps, despite the playback saying 224.
Resetting the connection default to 384 seems to have cured the
problem after a couple of reboots and I can now see it in full-screen
video, admittedly a little blurry but with full motion, though the
playback still says 224.

John Dann
www.weatherstations.co.uk