Dubb allows users to send video text messages in two different ways.

You can send video text messages from your mobile device using the Dubb Mobile app, your default text message application, or other SMS applications.
Here's a video with instructions for sending using the app:

You can also send video text messages through the web application one at a time, to groups, or through Dubb's Automation, by connecting a third-party service like Twilio, or Amazon.

Here are instructions for sending through the Dubb Platform:

https://support.dubb.com/article/60-video-sms-configuration-and-setup