We highly recommend that you turn on the captions whenever showing a video in class. Subtitles aren't just for students with hearing impairments. Subtitles can help everyone watch your video when their sound must be turned off, or when they want to use the subtitles to rapidly search through the video for specific information. YouTube can also translate your subtitles into many languages.
You can use YouTube Video Editor to manage the subtitles on your videos. Here are some resources for subtitles on YouTube:
Teachers should always be mindful of student privacy. Fortunately, YouTube Video Editor has a built-in blurring tool that can be used to blur faces or other objects from a video. To learn more about YouTube's blurring tools, click here.
YouTube Video Editor lets you add an audio track to your video. You may upload your own audio file, or choose from a library of Creative Commons music files. For more information, read this tutorial.