[FFmpeg-user] Inserting Seekable Offsets in m4a Audio File

[Budgie]

Hi, first post here and as will be apparent I am not a coder so please 
forgive naivity.

I have a number of audio files downloaded from Radio 3 using GiP which I 
have been told contain only 1 offset: the offset of the start of the 
audio track within the file (after all the metadata) and therefore the 
seek mechanism of the player I am using does not work.

The files are mostly over 2 hours playing time in good quality stereo 
but it would be good to be able to stop and resume rather than have to 
play from the beginning each time.

I believe it should be possible to use ffmpeg to remux these files and 
insert offsets but a simple command

ffmpeg -i inputfile.mp4 -c:a copy outputfile.m4a did not work.

Please could somebody help me understand how to fix this and hopefully 
preserve the metadata as well.

It would be good also if somebody could explain how I could find out for 
myself about how to examine the file and the offsets.  I am running 64 
bit openSUSE 13.2 with KDE desktop.

Regards,
Budgie2