Firstly, you must make sure that you have uploaded the video you want on your website to your website-creater hub.
Next, include the video tag in your HTML5 coder. You are able to format the video's width and height using the elements of the same name. You should then include the "source" tag and add the file name after the src attribute. Before you include the ending angle brackets, you must state the file type using the following code,"type="video/mpeg"." Here is an example of the code, the files name is file.mp4.
Along with this basic video code, you are able to add attributes to adjust how the video is played. For example, if you add the "controls" attribute at the end of your video tag (this goes for all other attributes as well), this adds video controls for you to use. This includes the play/pause button, a slider for time positioning, and the ability to change the volume of the video.
Since Neocities doesn't support video upload, we must use another method to include a video in our website. When you go to a Youtube video, click the share button and then embed. Leave everything as is and click the copy button provided. Then, paste the code into your HTML file and you've got yourself a video!