(NB This question is largely a duplicate of Best video codec for filmed powerpoint presentation but that question is 7 years old and I hope to see if there is new advice. I don't have enough reputation to comment)
I have to export a Powerpoint presentation to MP4 (specified by a conference organizer so non-negotiable). The presentation is 15 minutes long. File size has to be <30Mb, with resolution preferably 1280x720+. Exporting the slides directly from Powerpoint results in large files, even when re-encoded with higher compression.
I have recorded the audio separately and can change the bitrate as necessary, but higher would obviously be preferable.
Since the image part of the video is essentially 20 still images containing mainly text displayed for a certain period of time, it seems it should be possible to compress the video to a smaller file size without losing much image quality. How can I go about this?