If your hosting provider has strict bandwidth limits, that could also cause playback issues for your users. Uploading to YouTube or Vimeo and embedding the video is usually the easiest workaround, but if you prefer to keep it hosted on your own domain, make sure your server settings allow proper video MIME types. If you need to convert your video to a more compatible format, check out this https://www.movavi.com/image-converter/png-converter.html. It also supports various file type conversions, which has helped me a few times.