I'm not sure. I actually uploaded the video to Google Drive temporarily and it probably decoded and re-encoded it and then I downloaded the file and uploaded that to the community. I think the first time I attempted to upload it it gave me an error that the file was corrupt and then the second time it worked. So my guess is there is something wrong with your computer somehow specifically with codecs. With the cost of those codecs Microsoft stopped pre-installing them on computers back in the early 2000's to save money on the OS. Which caused some issues when people were trying to make audio files. I assume the same might have happened with video files. So perhaps you could do the same thing I did with Google Drive and see if it will work but uploading and downloading if you encounter an error. Even if I had direct access to your computer that error looks like a couple things so we'd have to rule out the various possibilities one at a time until we isolated the issue.
Can you take a screenshot of the file properties? While it may be a mp4 file it looks like there is something unknown about it. Codecs are important so that it can be decoded. Perhaps you can convert it to a .mov file type and see if it will upload?
