mp3wrap tmp.mp3 1.mp3 2.mp3 3.mp3

ffmpeg -i tmp_MP3WRAP.mp3 -acodec copy result.mp3 && rm tmp_MP3WRAP.mp3

Кодируем 320K в 128K
ffmpeg -i podfm_vstruju_05.mp3 -ab 128k podfm_vstruju_05_.mp3