How to
create button
link it to a file, uploaded through the create button context menu
save
copy link from button
paste the following code into a code node from Squarespace, replacing the URL with the just copied one:
<center>
<video style="width: 100%"
playsinline muted autoplay loop
src="URL-HERE">
<source type="URL-HERE">
<body oncontextmenu="return false;">
</video>
</center>