added video to keynote - it plays half and squashed in presentation

hello

i created a presentation that contains some videos that were recorded on mobile phones. they are mp4 videos.

in editing mode (i.e. when creating the presentation), the videos work fine.

however, when presenting, the video is squashed into half of the space, which is now black.

i have no idea why this is happening or what to do.

i tried this on two computers with the same outcome.

thanks