Create unique name for recorded videos

Now application creates a video named "output.mp4". The task is to create a unique name in the following format "SR_DDMMYYYY_%%%.mp4"

DDMMYYYY represents the date, month and year.
%%% represents three digits start from 000 to a maximum of 999.

If the system date is 14-feb-2018, then the filename should be
example names are: SR_14022018_312.mp3