To download video, visit the video info page, and then click the MP4 or source file.
You can also allow public downloading of videos. To to this, click the "Allow Video
Once this is done public viewers of your video can download the video file.
To download video replies:
Visit the video page that was used to collect the reply, click Video Replies, then click download.
If you are downloading video replies they will only be available in webm format.
Dubb provides a free converter https://dubb.com/tools/convertor that can be used to convert webm files into mp4 files.