Issue when uploading video, the sound cuts off

gertawbg_Stream 

Stream (Classic) is eventually going to be retired. We are likely to announce a date with 1 years notice later this year or early next. Https://aka.ms/streamroadmap 

Can you try to upload your video to SharePoint or OneDrive and see if it h a s the same problem?

If it doesn't work in SharePoint or you can't use that solution, work with your admin to open a support ticket. It sounds like there is something funky with your video itself.