Handling of simulcast attributes with multiple choices in a version seems to be underspecified #2769

ie; a=simulcast:recv 1,2,3;4,5,6;7,8,9

This is legal syntax, and its meaning is:

"I want you to send me three simulcast streams. For the first stream, you have a choice between rids 1, 2, and 3. For the second, you have a choice between 4, 5, and 6. For the third, you have a choice of 7, 8, and 9."

We obviously do not support this "multiple choices" semantics, so it is sensible to just pick the first choice whenever there are multiple, but I don't think we have written that down anywhere.