Looking at your question and requirement which you are trying to achieve I would simply say "YES" it is possible to make such a portal on the Magento platform.
Magento by default supports downloadable products which allow you to showcase sample videos to the customer and once they do payment then they can able to download from their my downloadable products section from my accounts.
For your second solution you can leverage the customer group for the general and premium customer segregation. Meaning those who have already purchase a membership you can move those customers to Premium customer group so that they have full access of all the videos.
Another thing is there are multiple extensions available for various membership options so you can use that as well.
Just one suggestion looking at the performance aspects - If you are planning to stream those video on this portal itself then I would suggest to stream/play those video on another server meaning keep 2 things separated logically - selling the membership and streaming the videos.
All the best for your new implementation and hope it helps !