If you need to shorten the long periods of silence in an audio file automatically, you can use “sox”, the swiss army knife of audio stuff.
sox input.wav output.wav silence -l 1 0.1 1% -1 2.0 1% \ && ffmpeg -i output.wav -codec:a libmp3lame -qscale:a 2 output.mp3
Reference: The SoX of Silence