It depends on the goal of the user:
- Does the user want to see a list of videos an scroll through it to search for inspiration (as you would do on a video portal)?
- Is the goal to see the newest uploaded videos to keep track on the new content?
I assume the first is true. In this case the user should not be bothered with the list changing (updating). The user should always have control over the system: see https://www.nngroup.com/articles/ten-usability-heuristics/
In an endless scrolling the loading new videos in the not yet visible area would not bother the user, but the area already scrolled should not change so the user can scroll back to a video seen before.
A different approach could be to show the user that new content has been uploaded an it can be seen by refreshing the list, this keeps the user in control and at the same time pointing to the fact that there is always newer content. (youtube does it this way)
Your second approach would be very annoying to the user. If the list (or gallery) constantly changes the user would not be able to view a particular video since it might change just in the moment the user decides to view a video.