AlterBrains

For Example, I have a site master.com and (slave.com or slave.master.com or master.com/slave)

master.com is a new/magazine site - I want registered level users to submit just an article or news but won't be able to submit videos
slave.master.com is a Media sharing website - I want all registered user levels to submit videos and pictures.

Note: I would like to use only one joomla installation for both site. Can I accomplish this with Mightysite? If so, how?

You can have a separate category for Videos and separate for Articles.
You can have 2 additional usergroups: 'Videos Publisher' and 'Articles Publisher'.
Categories can be configured to allow submit for one of these specific usergroups only via usual Joomla ACL.

For one Joomla installation I recommend last two case studies:
https://alterbrains.com/joomla-extensio ... se-studies