Can we save MP4 file using file upload and use it in UI?

I don't believe there is a way to directly play a video stored as an Appian Document (uploaded by the user). As you noted the a!videoField requires that the a!webVideo is hosted at some URL. If this is a requirement then you may need to find a way to programmatically take the user's uploaded video file, host it somewhere, and then use a!webVideo pointed to that URL. 

I don't believe there is a way to directly play a video stored as an Appian Document (uploaded by the user). As you noted the a!videoField requires that the a!webVideo is hosted at some URL. If this is a requirement then you may need to find a way to programmatically take the user's uploaded video file, host it somewhere, and then use a!webVideo pointed to that URL. 

If you need the url, you can experiment with "/suite/doc/<docId>", being the docId the video you have just stored in Appian

I have not tried to be sure but the docs page for a!webVideo says "Appian documents cannot be used as the source video."

Hi,  
i tried by giving document source but the video just appeared black screen rather than playing

Thank you Dan Lluhi , will try this.

David's proposed context, as seen above, works for me - "[environment]/suite/doc/[docId]".  That's not what you have in your screenshot.

Edit: I like Yogi's suggestion below - I'd personally forgotten about the (newer, i think) "url" option for the "document()" function, but this is ideal because it constructs the URL for us automatically, and (for what it's worth) encrypts the Doc ID in the resulting URL.