The command expanded to multiple lines as if written in a script:

L=5    
while true; do
  readarray -t paths < <(find . -type f -print | shuf -n 1)
  for i in "${!paths[@]}"; do
    path=${paths[i]}
    if ffprobe -i "$path" -show_entries format=duration -v quiet -of csv="p=0" > /dev/null; then
      N=$(ffprobe -i "$path" -show_entries format=duration -v quiet -of csv="p=0")
      D=${N%.*}
      P=$((D / 100 * 25))
      R=$((1 + RANDOM % D - P * 2))
      S=$((P + RANDOM % R))
      W=$((R / 4))
      LEN=$((1 + RANDOM % L))
      mpv "$path" --start="$S" --length="$LEN" --fs &> /dev/null
      W=$(bc <<< "$LEN - 0.5")
      sleep "$W"
      unset 'paths[i]'
    fi
  done
done

Usage:

• Open a terminal
• Change to the directory in which you have videos
• Run the command, changing "L=5" to some other seconds

The script assumes several non-standard utilities are installed in the system:

• shuf
• ffmpeg
• mpv