Is it possible to add a video file, but only allow students to view the file not download the file?
It is next to impossible to keep audio or video from being downloaded from the web. You can however make it a little harder in Canvas by using the Rich Content Editor and a feature in it called the Record/Upload Media Files button. Here are the instructions to use that tool: How do I record a video using the Rich Content Editor?
Here is something to vote on if you are of the mind to do so
Make a file read-only but Not Downloadable in Canvas:
ohhh, that is a 'big' link
REALLY big link
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