Rocket Validator looks for accesibility violations on your pages using the axe-core accessibility engine, hosted on our own servers and integrated into our web crawler. You don't need to buy an additional license, everything's already included in your Pro account at Rocket Validator.
A11Y check: video elements must have a track for captions
Accessibility rule: An HTML5 video element must include a track element with kind='captions' set as a property. The captions should convey all meaningful auditory information in the video including dialogue, musical cues, sound effects, and other relevant information for deaf users.