Sylvia/docs/doc 866

@mhoeber @lamagnifica Just need quick thumbs. This is the text that was beaten into submission earlier today.
I read both of these xref sections and I'm a little mystified. Where is the "Downloadable" option described? I only see the option to make transcripts downloadable. 
I think, in this case, it might make sense to indicate what the xrefs actually provide in the way of more info: For more information about the options for hosting and configuring videos, see...