You are aware you can open a video on start page now by setting your folder as
link? It would only display the video though, and not thumbnails below it of course ... More info on that here:
https://www.photo.gallery/documentation/lightbox/
https://www.photo.gallery/documentation/video/
Also, why not use Vimeo for your video? They have faster servers than yours, and the visitor can choose resolution (HD/SD) ...
If you gonna embed local mp4 file, try this:
javascript:lightbox('imagevue.php?a=video&path=folder/file.mp4');
Keep in mind the path is relative to your content folder, and thats where the video much be also. For example for the coe above, your file would be located in
content/folder/file.mp4.