Playing a video in the middle of your speech can provide a refreshing break to regain the attention of the audience. They can also be used to bring into the presentation an outside speaker to confirm your message, such as a customer providing a testimonial.
An enormous number of video options are available from school and public libraries and commercially. These require either a DVD, VCR or a CD-ROM player and a monitor, which are readily available either from the hotel where the speech is taking place, the hosting group, or a local A-V store.
However, unless you place multiple monitors around the hall, you will have a limit as to how large an audience can readily see the video (also check that the audio can be heard clearly every-where in the room).
Remember that you are not supposed to be showing any ads or motion pictures without permission, especially if you are being paid to speak. These are copyrighted and companies do not take kindly to having you use their creative work for your personal benefit. Fortunately, there are sources for royalty-free film clips (more on this later).
Of course, you can create your own videos, but only if you either can keep it simple or if you have experience or training to create a professional-level quality.
Never assume any technology will work! Get to the lecture hall early and check electrical outlets, cord length, the remote control device, microphone, laptop and projector, and Internet connection, if required. Bring extension cords and extra bulbs.