I am currently looking to convert my FLAC library to AAC for various reasons (space, my phone, etc.). The thing is, I can't seem to find a converter that will work directly from .FLAC to .AAC, I found one but only seems to work with .WAV and the people over at Head-Fi aren't very useful either. "Why change from .FLAC?" ".FLAC way better than .AAC" and such. So tell my guys, is there really a .FLAC to .AAC converter? or should I give up and use a .WAV to .AAC?
I use FormatFactory for most of my conversions. It supports most file types, has multi-threading support, converts most formats to any other applicable format, is freeware, and gets regular codec and software updates. Just be careful of the bit rates and what not in the defaults, they're kinda low for some file types.
I second this, I no longer need any sort of converter since foobar pretty much does most of it, and the things it can't do (like PCM -> FLAC) I can just find command line encoders for foobar to use anyway.
Take a look at ffmpeg, it is very convenient for all sorts of conversions, is very well documented and has a helpful community channel on freenode irc.
It supports decoding and encoding of both flac and aac, so you're ready to go. It works in both Linux, OSX and Windows.