Number of Google video formats on YouTube and content network is growing as much as their technical specifications are evolving. Keeping up-to-date can be a difficult task. Following infographic should help you orientate across the numerous basic atributes of formats publicly available in most countries.
Even now, there are most likely new formats being developed and tested as limited access ALPHA and BETAs. As soon as they become public, this infographic will be updated.
2019 Q2 update: Specific version of Masthead can now be purchased in Google Ads on a CPM basis.