Drupal 8 upload and embed a video to WYSIWYG
For simple solution Just get video_embed_field which includes module  Video Embed WYSIWYG Enable both of them. You will get options to configure your WYSIWYG here admin/config/content/formats/manage/full_html. Just add the Video button in toolbar and checked the option Video Embed WYSIWYG. I hope you get what you want.
Thanks