You can play audio-visual material including commercial DVDs (unless you have entered an agreement, such as a rental agreement, which only allows personal use) in a lecture/teaching context as long as only staff and students are present.
You cannot make a copy of a commercial DVD in any format without obtaining permission from the copyright owner.
This also means you cannot record any part of a lecture where a commercial DVD is shown using any recording software. The lecture recording must be paused while the DVD is being played.
This also applies to audio-visual material made available on the internet (except for podcasts by Australian broadcasters, which can be copied under Part VA provided the material has already been screened).