John Frizelle I think the use of word 'collateral' was commonly used by feedhenry to refer to anything that wasn't code. I don't believe it's appropriate (http://www.dictionary.com/browse/collateral) and I'm happy with calling video "documentation", but if a generic word is necessary, it's all "content".
There is a case for 'collateral', but would you consider it confusing when used for docs collateral? eg https://github.com/mairaw/Microsoft-Docs