Quadruple Sudoku (Daily Sudoku League #157)

I wanted to post another Sudoku today. However when I saw the Quadruple Sudoku in the 3rd round of the World Puzzle Federation Sudoku Grand Prix 2016, then I decided to post this Quadruple Sudoku which is made by me long back. Hope readers will enjoy this puzzle and this Sudoku will be good practice for this test. As this is my first Sudoku of Quadruple Sudoku type, I am looking forward to feedback regarding this Sudoku puzzle :).
Quadruple Sudoku is one of the standard Sudoku variations and this puzzle is around here for so many years. However, this is the first time I created this Sudoku type. This was because creating this Sudoku was easy. However, creating the image of this Sudoku type was tough. In fact, it took me more time to create the image of this Sudoku than to create the actual Sudoku puzzle. Anyway, this Sudoku has come very nicely with a good and interesting solving path.

This Quadruple Sudoku, I am posting in the Daily Sudoku League as the 183rd puzzle in this series. Can you solve this hard Sudoku puzzle?

Rules of Quadruple Sudoku

Apply Standard Classic Sudoku rules. Additionally, each set of four small numbers in the intersection of two lines indicate the numbers that are in the four adjacent cells.