Help with downloaded radio file formats and thumbnail jpgs please.

[Alastair]

I am getting into difficulty with tagging and then making some radio broadcast files work on 
my Twonky server running on NAS box.  

I have no trouble with mp3 files so if BBC programme is available as podcast I can 
download that and it usually is correctly tagged so can go straight on to NAS data base.

Similarly I have put some of my CDs of radio shows onto NAS having ripped and encoded 
them as flac files and tagged them myself and these work fine with Twonky.

Where I am having problems is with downloaded radio shows which are saved as .m4a 
files which I understand to be MP4/AAC files.  I could convert these using soundKonverter or 
similar for example and in future I assume I could include --aactomp3 in command line 
(not sure how with --pvr mode as cron job.  Put in preferences perhaps?)  However for 
classical music I would rather use a lossless mode of compression which works with 
Twonky etc. such as flac.   Also the files which come as m4a seem to lack any tagging 
whilst mp3 podcasts come with extensive tagging.  Does that mean I must include a 
tagging preference as well?  Please could somebody advise on what defaults should be 
and possible options.  I have read --longhelp but am still not wise enough!

Finally please could I have guidance on how get_iplayer handles jpg thumbnail files.  I see 
that these are downloaded at the end of a programme and then vanish.  What am I doing 
wrong please?

Alastair