Run macro on each frame in beamer

Question

How to patch the beamer \frame command (frame environment) so that \note{} is executed on every frame. This question is closely related to this one, however, I want the additional macro (\note{} in my case) to be executed not before but on every frame, that is:

\begin{frame}
    % empty dummy note, ensures that beamer renders a note page for this frame
    % if compiled with \setbeameroption{show notes}
    \note{}

    % frame content (may contain "real" \note commands, which accumulate)

\end{frame}

I am trying to achieve that in the resulting PDF every slide (even from frames that do not specify notes) is followed by a notes pages, so that I can use pdfnup --nup 1x2 (or similar tools) to pair them on the same page. That is, the following minimal example should result in a 4 page PDF file:

\documentclass{beamer}
\setbeameroption{show notes}

\begin{document}

\begin{frame}{Slide with notes}
  Slide content
  \note{Cool note!}
\end{frame}

\begin{frame}{Slide without a single note (a notes page should follow nevertheless!)}
  More slide content:
\end{frame}

\end{document}

Side note: I do not want any solution that builds on pgfpages (such as "notes on second screen"), as this package interferes at the shipout level with the textpos package, which I absolutely need for absolute positioning. The results look "funny" at best!

Any ideas are welcome!

Answer 1

This seemed to work for your small example:

\makeatletter
\def\beamer@framenotesbegin{% at beginning of slide
  \gdef\beamer@noteitems{}%
  \gdef\beamer@notes{{}}% used to be totally empty.
}
\makeatother

Mind you, I've not put too much thought into it, so complain if it doesn't work. :)

Answer 2

One sneaky way to do this is to put the code somewhere else that gets evaluated each frame rather than to try to hook in to the frame environment itself. For example, the templates can contain arbitrary code so you could redefine one of the always-used templates to include the relevant command.

In a similar circumstance, I've hooked in to the \frametitle command as that's a bit more robust. I don't know if \begin{frame}{Some Title} calls \frametitle internally so I don't know if this would work for you.

Answer 3

Perhaps the easiest approach would be to create a wrapper environment. Basic example:

\documentclass{beamer}
\newenvironment{nframe}[1]{%
\begin{frame}[environment=nframe]\frametitle{#1}\note{}%
}{%
\end{frame}%
}
\begin{document}
\begin{nframe}{Title}
  Foo
\end{nframe}
\end{document}

I think this currently breaks if you don't supply a frametitle, which is awkward... Leave the second argument empty to not have a frametitle.

---

Here's a solution that apparently doesn't work, I keep it up here for the sake of posterity.

Adapting the answer in the linked question, could you not use etoolbox's \appto like so: \appto{\frame}{\note{}} to include a note at the beginning of each frame?