how arguments works?

[jpalvaradomil]

I try to execute this command

ffmpeg -i track.mp3 -af silencedetect=noise=-30dB:d=0.5 -f null out.txt
using the command line in my ubuntu pc instalation works fine
but this failed when I use the ffmpeg-worker-webm.js

the error:

Duration: 00:01:32.20, start: 0.000000, bitrate: 64 kb/s
Stream #0:0: Audio: mp3, 44100 Hz, mono, s16p, 64 kb/s
Automatic encoder selection failed for output stream #0:0. Default encoder for format null (codec pcm_s16le) is probably disabled. Please choose an encoder manually.
Error selecting an encoder for stream 0:0

thinking that the cause of the error was the version shipped (4.4) I succesful compile ffmpeg.js using the tag n5.1.6 from the git ffmpeg, but i obtain the same error.

In conclusion
how to arguments works?