You don't say what problem you're trying to solve, so it's not easy to provide a useful answer.
I presume you're trying to provide arguments to ffmpeg?
'--useragent test' won't do anything useful, because nothing out there that cares about user agents is going to recognise 'test'.
A quick google will find several sites that list valid useragent strings. Remember to quote them properly if using them on the command line.
e.g.
If the user agent string is "foo bar (1234)" you'll need to use:
--useragent foo\ bar\ \(1234\)\r\n
Needless to say perhaps, if you're getting streams already, you probably don't need to bother with setting a user agent.
