Sometimes the room is so large that the screen dwarfs the presenter.
Your slides will be on the big screen and easy for the audience to see but you need to do is make sure that that audience can see and connect with you.
The trick to this is to move around, our eye will always want to follow a moving object instead of something static like a screen. This is not to say that you should be constantly moving around but plan your stage movements in advance, move to one area of the stage and make your point then move to another area for the next section. Use hand gestures to help convey your message.
What a number of venues do is solve the problem of a large room is to put the speaker on the big screen too, which is brilliant, the audience can see you properly, they can connect with you easily and listen more.
There’s a downside too, they usually try to squeeze you and your slides onto the same screen. This could potentially mean that it will be more difficult for your audience to read your slides.
If you can, go to the venue in advance and see how it will work and what their plans are for your presentation. If you can’t visit the venue, then contact them and find out.
The best solution is to be able to switch between your slides and you, this may require an assistant being on hand to switch between the slides and the video, it will also help you ensure that your audience is focussing on you and your message.