Try this:
Use a file explorer software to navigate to the directory where the video is located. Then click on it and it will ask you what you want to use to open the file. I think "Video Player" or "android system" should appear. Pick one. And whichever works, open it again from the file explorer and check the "Use this program as default" box.
Then when in gallery or the recorder, the file will play when clicked on.
