Uploading Videos to Webinars

We seem to consistently have issues uploading videos (MP4) to webinars in the "Engage your Attendees" section.

Either the video takes an incredibly long time to upload, or it doesn't upload at all. The MB count will eventually reach the end, then the screen will switch to "uploading" and the video won't actually upload.

We never upload more than one video and they are well below the size limit of 4GB. I've tried renaming the file names as simply numbers, and sometimes this works, but today it didn't. I've spent all day trying to upload a video for a webinar tomorrow, and in the end it worked on a colleague's computer but it took her a very long time as well.

Are there any tips or tricks that I'm missing here??