Given your scenario of serving the right video to browsers, you shouldn't need to do UA sniffing because the browser should have the right accept headers so you can do proper content negotiation.
UAs these days should only be good for one thing, which is analytics. The browser should provide all the necessary information for other stuff through its other headers, such as Accept. Of course, I emphasise should because there's a wee bit of fantasy in that statement.
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Given your scenario of serving the right video to browsers, you shouldn't need to do UA sniffing because the browser should have the right accept headers so you can do proper content negotiation.
UAs these days should only be good for one thing, which is analytics. The browser should provide all the necessary information for other stuff through its other headers, such as Accept. Of course, I emphasise should because there's a wee bit of fantasy in that statement.