?Readers Digest Version?

Over and Over again no matter how you enter things the code will get changed for whatever reason I have no Idea.  I can spend hours trying to work around it but cna't figure out for the life of me why it does this so please someone tell me why this is and is there a way to TURN IT OFF.......One example is to try to embed a video in the online store and not even a direct post into the database will produce a video explaining what the product is.  This is just trying to use the very powerful technology this site offers.  I can't tell you the frustrations that are had from seeing something look so nice on the frontside and then be destroyed by some kind of code corrector............Anyone please explain what the idea is behind this as I want to do is stop repeating the same work over and over again.......