Trouble in Cut a portion of an audio file, and add fade in and fadeout Effect
Your command is wrong, use this one: ffmpeg -i track1.wav -ss 00:00:38.160 -t 00:00:20.720 -vn -codec:a libmp3lame -ac 2 -b:a 256k -map a -af afade=t=in:st=38:d=3,afade=t=out:st=55:d=3 output.mp3