As noted, video messages are not stored on the device. Luckily for us, they can be accessed via the internet. The first step is to verify that a video message was sent, by looking in the Messages table in the body_xml column. Next, note the convo_id field for the message:
Our video message is in convo_id 257.
Then, look in the Chats table for that convo_id in the conv_dbid column, and find the dbpath value. This will be the name of the conversation's backup file:
To find the backup file, look in files/<username>/chatsync. There will be a folder for each conversation, the name of the folder is the first two digits of the backup name. Our backup will be in folder 28.
Open the backup file in a hex editor, and search for videomessage. You should find a URL and a code to access the video:
Actually accessing the URL may require an additional warrant or legal permission, depending on your local jurisdiction. As this data is not on the device, and is private, viewing it without legal guidance could invalidate any evidence found in the video.