Generating random filenames in ffmpeg output

hello guys I am using ffmpeg to output different output filenames. By some googling, I did find a command to generate random strings in shell. I used tha in my own command like this:

ffmpeg -f concat -i gif-list.txt -c copy cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1.mp4

But this is not working. How can I achieve this?