When using videos in class or online they need to have captions which are 99% accurate.
If you have created your own video using Kaltura Media within Canvas, these directions website can help you.
If you created your own video and are using YouTube, these directions from the COLRS website can help you.
If you are using a video on YouTube which you didn’t create and is not captioned, you can use a secondary website like Amara. Amara allows the video to remain located at YouTube, but allows you to route the video through their site and add the captions at Amara, so there is no copyright issue. You can even search Amara to see if your video has already been captioned there.