Experimental HD and audio only downloads

[fred.d]

I've found that a lot of content seems to be available in the new Full 
HD format. However every so often I come across one that downloads only 
the audio. Playing with parameters and download method doesn't help so 
I'm guessing it's the far end.

Anyone know if this is a get_Iplayer thing or is it simply that the 
files on the BBC sites aren't 100% when it comes to this quality?


Ta.