R Markdown version of \framesubtitle?

Question

The following is the least TeXy way I know of to create a beamer slide with a subtitle:

---
output: beamer_presentation
---

### Title of Slide
\framesubtitle{Subtitle of Slide}

Frame content.

Is there a way using no LaTeX, or does R Markdown not directly support slide subtitles?

Answer 1

Markdown doesn't support \framesubtitles. It assumes you'll use the regular markdown #'s to denote sectional units, and a specific (highest) level is used for frame titles. Anything lower than that will only create headers within the frame, but not a subtitle. From the Pandoc Manual (based on a specified --slide-level or the default):

The document is carved up into slides according to the following rules:

• A horizontal rule always starts a new slide.

• A header at the slide level always starts a new slide.

• Headers below the slide level in the hierarchy create headers within a slide.

• Headers above the slide level in the hierarchy create "title slides," which just contain the section title and help to break the slide show into sections.

• Content above the slide level will not appear in the slide show.

Of specific interest here is that "headers below the slide level in the hierarchy creates headers within a slide." These headers are actually block environments, since the following minimal markdown

---
title: A title
output: 
  beamer_presentation:
    keep_tex: true
    slide_level: 1
---

# Title of Slide
## Subtitle of Slide

Frame content.

creates a .tex file:

\title{A title}
\date{}

\begin{document}
\frame{\titlepage}

\begin{frame}{Title of Slide}

\begin{block}{Subtitle of Slide}

Frame content.

\end{block}

\end{frame}

\end{document}

If your presentation is fairly simple, you can trick LaTeX into converting a block environment into the \framesubtitle. Add the following file (call it block-to-framesubtitle.tex) in your working folder:

\usepackage{environ}
\RenewEnviron{block}[1]{\framesubtitle{#1}\BODY}

Now you can use

---
title: A title
output: 
  beamer_presentation:
    slide_level: 1
header-includes:
  - \input{block-to-framesubtitle}
---

# Title of Slide
## Subtitle of Slide

Frame content.