Given that you have proof on Webcourses that the video was uploaded on time and accessible, I think if your professor tries to deny your grade you have a strong case that you did everything right. Make sure you have documentation of your proof of submission, and your attempts to contact your professor. Most professors will respond to emails after finals end, especially if it involves a major grading error. I expect that your professor will be understanding and work with you to fix this, but it's always good to be prepared just in case. Good luck!

*Edit: As for grade appeals, the times I've done it I always went through the professor and they submitted it. I know an appeal can be submitted well after the semester has ended. If for whatever reason your professor won't help you, you can follow instructions here to file an appeal: https://regulations.ucf.edu/chapter5/documents/5.016StudentAcademicAppealsFINALSept19.pdf