I want to use my front end aplication to watch the CCTV cameras using Milestone

If using .NET is possible I recommend the ImageViewerWpfControl

https://developer.milestonesys.com/s/article/exploring-the-MIP-SDK-recommended-top-SDK-samples

https://doc.developer.milestonesys.com/html/index.html?base=samples/playbackwpfuser.html&tree=tree_2.html

If not using .NET there are other options.

Mobile Server and Mobile SDK.

https://doc.developer.milestonesys.com/mipsdkmobile/

C++ Toolkits.

https://doc.developer.milestonesys.com/html/index.html?base=reference/architecture/cpp_development.html&tree=tree_2.html

Native protocols -Image Server

https://doc.developer.milestonesys.com/html/index.html?base=reference/protocols/imageserver_index.html&tree=tree_3.html