Video ID

Eleven characters of letters, digits, hyphens and underscores. Every tool, embed and API call uses it, and it stays with the video for life: change the title, the thumbnail, the description or the privacy setting and the ID is untouched. That is also why you cannot swap the file behind a published video without losing the URL, the views and the comments. It is case sensitive, so an ID copied out of an email that mangled the capitals sends you nowhere.