Converting xaringan presentation to beamer

Question

I wrote a very long complicated presentation in xaringan, so I have the underlying rmarkdown file as well as the compiled html.

For reasons of collaboration (the things we do for co-authors!), I need to switch the presentation to beamer. I know xaringan compiles into markdown as a first step before compiling to html. I was wondering if there was a way to compile the xaringan rmarkdown file to a format I could then convert to beamer using pandoc/knitr/rmarkdown etc? Even halfway solutions that get me most of the way to valid beamer code would save me loads of time.

I tried:

rmarkdown::render('file.Rmd', output_format = "beamer_presentation", output_file = "test-beamer.pdf")

but it doesn't compile and the intermediate .tex is a mess: it doesn't recognize -- as an incremental slide progression, etc. nor really would I expect it to.

Has anyone tried to commit this particular mistake? Is there a way to, say, convert an rmarkdown document in xaringan syntax into an rmarkdown presentation that could target beamer as an output?