Indeed - and I know several experienced conductors who place a video camera behind the performers when they're conducting concerts. This gives them a chance to review it afterwards and see where they can improve what they do.
I think video can be very useful as you're gaining experience. You soon forget it's there so get on with the job of conducting then when you review it later you can easily see where you're gestures are unclear, confusing, inconsisent or unnecessary (e.g. 'mirroring' with both hands).
One further thing I'd suggest is try to get the chance to do some orchestral playing. Often the people who conduct good amateur orchestras are excellent. I've been lucky enough to play for John Anderson (MD for Brassed Off and internional freelance conductor), Gary Walker (now regularly conducting RPO and RSNO), David Angus (International freelance conductor), Ben Ellin (young freelance conductor) and Natalia Luis-Bassa (professor of Conducting at RCM, Mentor for Peter Snow in Maestro). These have all been relatively young but talented conductors working with amateur orchestras early in their careers. As an orchestral brass player you ahve plenty of time in rehearsals when you're not playing - an ideal opportunity to study their conducting technique and rehearsal technique!
Of course, if you can't get orchestral playing, most amateur orchestras are still happy for people to sit in on rehearsals. If you find a conductor you like, tell them that you're interested in conducting and dveelop a relationship with them. Get your own copies of scores and they may even be happy to spend 5 or 10 minutes chatting to you about the music and their approach to it.
Pete