Convert all files but not those already in selected destination format

Hi,

I need to convert songs to MP3 because my car only support this file format. However, I would like to avoid re-encoding files that are already in MP3, whatever the bitrate/quality : is there a way to automatically skip conversion of those files that are already in the proper format? It is very time consuming to check which format is used in every folder…

If not, should I request an enhancement (I am thinking of an option like "do not convert files that already have the desired extension")?

Regards,
Yvan