Video overlays

[jpreiss]

Lack of robust video support is the biggest drawback of Beamer versus PowerPoint, Keynote, etc. pdfpc somehow makes it work. It would be nice if we could, too.

[jpreiss]

Experimental video support has been added in branch videos: https://github.com/jpreiss/pypdfdeck/tree/videos. It seems to work pretty well so far.

It requires a modified version of the pdf2image library that supports extracting the embedded URLs from the PDF. This is currently in draft PR at Belval/pdf2image#257.

If we can get this PR accepted, we should merge video into master.

If not, we can consider reimplementing some of pdf2image's functionality locally, but that would be a bit ugly.