Batch convert to m4a

Hi,

I am on ubuntu 12.04 and have installed the gstreamer plugins so that, through the GUI, I can convert flac files to AAC (.m4a). I have to, however, convert a large set of directories and rather than do it by hand I was planning to run a shell script that converts the files from all directories and moves them to appropriate target directories (which are of course all different). Therefore I wanted to use soundconverter From the command line.
But.. it first took me a bit to find out what 'mime-type' to use to get .m4a. From looking in the code I am guessing it is audio/x-m4a.
However, when I do a test I get this error/output:
soundconverter -b -m audio/x-m4a -s .m4a testfile.flac
...
Traceback (most recent call last):
  File "/usr/bin/soundconverter", line 2965, in <module>
    main(args)
  File "/usr/bin/soundconverter", line 2961, in main
    cli_convert_main(args)
  File "/usr/bin/soundconverter", line 2926, in cli_convert_main
    c.init()
  File "/usr/bin/soundconverter", line 1243, in init
    encoder = self.encoders[self.output_type]()
  File "/usr/bin/soundconverter", line 1364, in add_aac_encoder
    (self.aac_quality * 1000)
TypeError: unsupported operand type(s) for *: 'NoneType' and 'int'

Also, is there a way for me to control the bitrate and output directory from the command line?

Thanks so much for any help,

Erik