Suppress Slack IRC 'voice' noise in Hexchat

I honestly appreciate Slack has an IRC option, but it's noisy: due to the intolerable amount of 'voice' notes, it's impossible to see actual messages. I'm using a ZNC bouncer, and the best would be to filter it there, but so far I could not figure out, how, so after a little digging, I've found this on Linux Mint forums¹:

( migrated from xchat to hexchat )

#!/bin/sh

# change directory to the desired one
cd $1

# create resized dir
# warning! if exists, the pictures will be overwritten!
mkdir resized

# look up files with extensions
for fname in *.*; do

  # this is the resize and slightly sharpen part
  echo "resizing $fname"
  mogrify -sharpen 1 -quality 96% -write "./resized/$fname" -resize 540x540 "$fname"

  # this is the watermarking part
  echo "watermarking $fname"
  composite -compose atop -gravity SouthEast "/path/to/watermark/image" "./resized/$fname" "./resized/$fname"

done