Sir,I am applying on a job on ireland and the agency is requiring me to get a registration number through brighcove.is it a scam.please answer.thanks

This sounds a bit strange. I'm Irish myself and have moved country a number of times, never had to register anywhere but with the government in question.
In some cases, as in the U.K. it's actually easier to get the job first and sort out the legal and tax issues through the company.

Going to or phoning your local Irish embassy or consulate would be a better route.
If you can't find an Irish embassy in country, any EU country embassy should be able to help.

Have a look here: http://www.citizensinformation.ie/en/moving_country/moving_to_ireland/working_in_ireland/coming_to_work_in_ireland.html