I have seen this code:
vol=$(ffmpeg -i "$file" -af "volumedetect" -f null /dev/null 2>&1 | grep mean_volume | awk -F': ' '{print $2}' | /cut -d' ' -f1)
echo "existing mean_volume.........$vol"
by https://superuser.com/users/390724/chris-prince dated sept 2015 here. I used it and works as intended for individual audio file. However, when trying to use it in loop to do a batch on multiple files it fails(no value for vol). I tried to get the answer in original thread but being told must start a new thread. I further tested the code. It seems problem is with in ffmpeg.
