Just one or two notes on how I got the module to work. With no documentation and limited Drupal and PHP skills it took a while.

- Make sure that SoX is working correctly on the server with mp3 decoding and encoding enabled. Many out of the box Sox installations including Ubuntu does not have mp3 encoding enabled default.

- SOX Executable Command: there is no mention of this but you need to have the following as place markers %videofile %convertfile in your script for the infile and outfile part of SoX scripts. To convert a WAV file to MP3 your settings for the 'SOX Executable Command' on the module settings page could be something like :

-r 8000 -c 1 %videofile %convertfile