A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Thanks Lyn,
I've found the problem. Although the narration remained on each slide, somehow the timings for most of the slides were wiped. I went into slide sorter view and in the slide advancement settings added the run time of the narration for each one individually. I also checked both boxes for 'on mouse click' and 'after'.
That's ensured that the video converts perfectly with each slide being fully narrated before transition.