I'm interested in adding the Gallery app to my suite. I'm testing a demo, now. I uploaded a video, and in the controls, downloading the video is allowed. I tried to use JavaScript to insert the "controlsList=nodownloads" attribute, but the JavaScript is not reaching the popup modal. Is there any way to control who or if a video can be downloaded?

document.getElementById("elGalleryVideo").setAttribute("controlsList", "nodownload");

Only works with the main page of the video, not the popup modal.

document.getElementsByTagName("VIDEO")[0].setAttribute("controlsList", "nodownload"); 

Seems to work with all video uploads, except the gallery popup modal.

Whether or not you can download a video is dependent on the browser (and plugins). While you could potentially add that line, as you mention, thats simply telling the browser not to add a download button. The reality is however, if the video is there, its able to be downloaded if the knowledge is there to do so