I'm using this command:
afconvert -f 'm4af.m4a' -d aac@44100 -b 48000 -c 1 filename.mp3
to convert my .mp3 files to .m4a files, sadly, the tag infos(artist, song name, album name, etc) and album cover are lost after the conversion, can I preserve these infos?
It seems that this is just just not possible, i.e. afconvert is too dumb. When I tried to convert aiff files to aac format I finally had to use iTunes for conversion, because afconvert loses all tags. You may consider filing a bug report to Apple.