Hi Sudhir,
In addition to all already said, you need to see what IS-Media can give and what you can get on ECC. As you mention, the company has decided to bring everything to ECC, it is ok but it can involve a lot of development and maybe at the end it could be more expensive (in cost and time) because you are doing all from scratch.
The advantage of IS-Media is that it is supported and tested by SAP and some processes are already developed.
In our case, the decision to use IS-Media was not so much by processes covered, but it was by the customer/material masters records, the integration and reporting data and brings the solution, for example the use of ISBN (check the new fields on master data: Media Product - Media Product Master - SAP Library). Also this is necessary to consider that some IS-Media processes require CRM system, for example, the intellectual property and royalties (check this link: Integration of SD Product Sales With IPM - Intellectual Property Management (IPM) Integration - SAP Library)
As well Sandip says, would be ideal to have an overview of IS-Media, I would recommend talking to SAP, in our case they were interested in selling this solution and helped us show IS-Media demos to the customer.
Hope this helps!
Regards.