First check if args are empty before checking if input dir exists.
Add a mapping of audio formats and extensions; add a 2d map of format and settings that returns ffmpeg args.
Add test for ffmpegArgs func.
Remove hard-coded ffmpeg args; Implement ffmpegArgs func; Make arg help clearer.
Add more debugging information for the -sim flag.
Use t.Fatalf at the end of reporting an error.
Update readme.
Rename files with various audio file extensions.
Improve TestIoPaths by testing different input parameters, not just the output file paths.
Simplify and clean audio input and output paths.
Merge bug fixes and improved tests.