You must make sure you have set up the correct sharing permissions on your video before you copy the link or your marker may not be able to view it. Do this by clicking on your video, and going to the 'share' icon underneath it.

Then select 'Share by web link'
Then select 'Options / Unrestricted Access - Always'

Then select 'Bypass Authentication'

Then copy the URL on the top left of the screen and use this link when submitting your assessment.

It's a good idea to try and open your link in an incognito browser window to check it is accessible. Remember - if the marker can't access your video, they are unable to mark it.
Always go back into the assignment after submission to confirm that the video has uploaded successfully. If the video shows as 'Coming Soon' you may have to wait a few minutes and reload the page.
Lower resolution will be good enough for almost all circumstances. Remember that for most assignments you are being assessed on what you are doing in the video, not the video itself.