Why Is youtube doing this to my videos?

Youtube seems to make my videos that look perfect after rendering in vegas
Pro look bad? It's only on high res minecraft texture packs though because the rest of my videos are fine

I see what you mean it looks a bit grainy, it seems like your settings in vegas are giving you problems, check your rendering, make sure it isn't changing the qualities too drastically. The Format you record in might be different to the one you are rendering in vegas. Check these settings as it looks to me like it is trying to convert a key part of your coding, what you have to remember is if it's giving you a MP4 file they are very compressed.

It'll be the coding.
You need to convert into a Youtube omtimised format.

I think that'd be down to you not having enough RAM or a powerful enough Graphics Card to handle the recording? Try on a better PC or maybe try playing in a lower res with that texture pack?