character encoding

Regarding our SRT discussion, here's a new question.  How does SRT handle different character encodings-- Windows, UTF-8, UTF-16, Shift-JIS, Big5, etc.-- without using byte order marks (BOM), which are *not* required by unicode?  In other words, how is a UA going to intuit character encodings if they are not explicitly declared (which they *would* be in an XML document)?

Thanks.
Geoff