Audacity tutorial: Converting to mp3 or AAC and other formats, example: Matthew Smith - epic orchestral synth music for film and game effects; Buanzo's LAME mp3 library
FFmpeg - Wikipedia
aac - Ffmpeg makes audio longer when changing bitrate - Stack Overflow
How to convert AAC/MP4A to MP3 using FFMPEG in full length? Audio file gets cut off after 1 second - Stack Overflow