Video activities

While investigating Opigno for our organization, we've run into some video issues we haven't been able to resolve. First is when uploading an MP4 video in the video activity type. Everything starts out fine- click on the upload a file, upload it, click on the link to watch it in a small window to verify success, and save the activity. When viewing the activity (to test or in a training), the video is not playable. We get a black box with a play button, volume, etc., that has 0:00 time and nothing is clickable. We've gone through this with a variety of videos with the same result. We can upload the same exact MP4 video as part of an H5P interact video, however, add interactions, and it all works perfectly. Completely confusing as to why it works for H5P but not in the video activity. The other place we've had issues is with the video activity type and external videos. We currently use Mediasite for streaming our live videos and that is where they live on-demand afterwards. We cannot link to those videos in the video activity type- we get an error that it can not find a video provider to handle the given URL. We have a handful of videos on YouTube as well, and those work fine to link to, but the majority of our content cannot live there. We were looking into both AWS and Google for video hosting, but are concerned since our current host is apparently incompatible- would these be? Does anyone know why we're having issues uploading MP4 videos in the video activity type? What else besides YouTube and Vimeo are y'all using to store external videos? Hopefully we're overlooking something very simple and fixable and can just deal with feeling silly for missing it. Thank you so much for any insights!!