The basic answer is this: Once a video passes 300 views, YouTube collects subsequent views on its central server, where those views are then verified to make sure they weren’t racked up by a bot, or through some other nefarious means. This verification process takes some time, about half a day or so. Once the verification process is completed on a batch of views, the view counter goes up.
As Hamilton said in the video below:
Views, as mentioned, are a currency. When you have a video with very small amount of views you don’t need to be too careful about what the view was. However, once it gets to be above 300 and beyond, this currency, we really need to verify and make sure that the number is what it purports to be. So this means that we have to go through a statistical verification process. And that statistical verification process actually takes some time. And thus we go from incrementing one by one, to then saying, OK, now we’re incrementing in batch. And all of these views we’re adding on have been verified by YouTube to be real views. We are preventing things like bots to go in and add a bunch of views to a video.
Ok, but why the number 301? That, it turns out, is simply the arbitrary threshold YouTube engineers set as the cutoff. Hamilton explains that the actual code YouTube has written for this process says that any views “less than or equal to” 300 can be counted without verification. This allows one more view to slip in before the doors are closed.
None of this is of much importance from a user standpoint, of course. But it is interesting to finally have an answer for one of those simple mysteries of the Web.