In order to download a video the "Allow Video Download" checkbox must be selected.
The Allow Video Download checkbox is available on the video editing page for the video you are trying to download
To download video, visit the video info page, and then select the drop down arrow next to the Edit button.
From here select Download Mp4.
This will provide you with the original source file.
If you uploaded the video as an MP4 you will be provided an MP4.
If you recorded the video using the platform it will be a webm file. However you have the ability to download it as an MP4.
If the video opens in a separate tab, Right click on the video and select Save as....
After you click download MP4, click the MP4 option next to where it says Download:
Here is a tutorial gif.