How to calculate the average difference between values ​​in SQL?

Question

MySQL

The structure of the table is as follows:

It is required to find the average difference between actions in time (timestamp) for each object (file).
For example File1 had 4 activities:
Activity1 at time 1549256689
Activity2 at time 1549655521
Activity3 at time 1550165431
Activity4 at time 1550317858
For example File2 had 2 activities:
Activity1 at time 1548548573
Activity2 at time
1549875732 File2 1327159, total average 973436
How to write a SQL query to find such an average difference?

Answer 1

I got a pretty top answer from Stack Overflow, the guys there understood everything without linking to references and sending to a simple avg function, the following came out:
Thanks to everyone who tried to help!
PS in the eighth version there is still a LEAD statement for iterations

Answer 2

https://dev.mysql.com/doc/refman/8.0/en/group-by-f...