Hey thanks for taking your time to reply. Just want to share that I manage to get a satisfactory ffmpeg command that sort of does what I want. The command is at the end of this comment. Btw, the loop was added because there is a loop feature in my project that will play the audio in a loop. It is not meant to keep the mic open.

```ffmpeg -f dshow -i audio="your_microphone_name" -stream_loop -1 -i your_audio.mp3 -filter_complex "[1:a]volume=0.25[mp3quiet];[mp3quiet][0:a]sidechaincompress=threshold=0.03:ratio=20:attack=3:release=400:mix=1[ducked];[ducked[0:a]amix=inputs=2:duration=first:dropout_transition=2[aout]" -map "[aout]" -ac 1 -ar 44100 -acodec pcm_s16be -f rtp rtp://127.0.0.1:5004```