Mp3sync

mp3sync lets you batch encode random MP3s to a single bitrate/samplerate/channels for use with SimpleDJ or other non-transcoding Auto DJs.
There are 2 main benefits of using this program over a shell script and the LAME MP3 encoder:

• The program also copies your ID3v1/v2 tags to the new file.
• If you leave your output folder alone mp3sync will only transcode new MP3s from your source folder.
  
  

Usage: mp3sync -i c:\source\music\folder -o c:\output\mp3\folder -b bitrate -c channels -s samplerate

bitrate is any legal MP3 bitrate (32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320)
channels is 1 for mono, 2 for joint stereo, or 3 for stereo
samplerate is any MP3 legal samplerate (48000, 44100, 32000, 24000, 22050, 16000). Default and recommended value is 44100.
Note: Remember MP3 restricts bitrate/samplerate to certain combinations!!!

You can also use mp3sync -h for more options...