This is a simple method to prepare a presentation as a video recording.
Keynote:
Prepare your presentation and notes exactly as you would normally do so
Find a quiet place and use the best microphone you have available. The one built into most headphones is adequate, and preferably to the inbuilt microphone on a notebook computer.
On each slide, use the inbuilt record audio feature under the menu → Insert → Record Audio
After the recording is finished, an Audio icon will be embedded into the slide. This can be selected and edited if required.
Select the audio icon, as well as any other media (movies etc.) and un-check “Start audio on click”
After recording audio for all your slides, go to → File → Export to → Movie
Select the highest resolution available, and “go to next slide after” 1 second.
Review the presentation and it’s length thoroughly before submitting.
Tips:
Leave a short pause at the start and end of each audio recording. This will make it easier to edit if required.
If you have video and audio in the same slide, the exported presentation will show the slide until all media has finished.
If there are elements of your presentation that require more advanced timing (if you have transitions on individual elements etc.), you can use the “Record Slideshow” feature. This allows you to go through the whole presentation click by click, and then export it as a move afterwards. Make sure you select mute while doing this, to avoid additional sound being recorded over the top of your pre-recorded speech.
If you have trouble with background noise, record your audio in Audacity or similar apps with noise removal tools, instead of the inbuilt keynote recorder.