One big difference, the comments are tied to the code, so if you change the code, it is fairly easy to change the comments, so the reflect the new code. Video, or any other 'external' documentation isn't so clearly attached. First, which version of the code does this documentation apply to, this matters a lot if you are 'documenting' internal details, and not public API. It also may be less clear that the video/other documentation needs to be updated, unless you add a comment like this section described in YouTube video wxyz. Also, editing a comment to reflect a small change is a small task. To 'edit' a video (to change technical content) tends to mean totally redoing it.