Beamer multiple appendices

Question

I am using the beamer class for a presentation and I want to include additional material for some contents as appendices.

MWE:

\documentclass{beamer}
\usepackage{appendixnumberbeamer}
\usetheme{Frankfurt}
\usecolortheme{beaver}
\useinnertheme{rounded}
\setbeamertemplate{footline}
{
\leavevmode%
\hbox{\begin{beamercolorbox}[wd=.3\paperwidth,ht=2.5ex,dp=1.125ex]{author in head/foot}%
\usebeamerfont{author in head/foot}\centering\insertshortauthor%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.6\paperwidth,ht=2.5ex,dp=1.125ex]{institute in head/foot}%
\usebeamerfont{institute in head/foot}\centering\insertshorttitle%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.1\paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm ,rightskip=.3cm plus1fil]{title in head/foot}%
\usebeamerfont{title in head/foot}\hfill\insertframenumber/\inserttotalframenumber%
\end{beamercolorbox}}%
\vskip0pt%
}%
\begin{document}
\begin{frame}
Content 1
\end{frame}
\begin{frame}
Content 2
\end{frame}
\begin{frame}
Content 3
\end{frame}
\begin{frame}
Content 3
\end{frame}
\appendix
\begin{frame}
additional material for content 1
\end{frame}
\begin{frame}
additional material for content 1
\end{frame}
\begin{frame}
additional material for content 1
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\end{document}

How can I get LaTeX to number each of the appendices indivudally? Using multiple \appendix commands does not work (the number of pages is not displayed correctly).

Answer 1

Based on https://tex.stackexchange.com/a/285383/36296 and https://tex.stackexchange.com/a/303757/36296

\documentclass{beamer}
\usepackage{appendixnumberbeamer}
\usetheme{Frankfurt}
\usecolortheme{beaver}
\useinnertheme{rounded}
\setbeamertemplate{footline}
{
\leavevmode%
\hbox{\begin{beamercolorbox}[wd=.3\paperwidth,ht=2.5ex,dp=1.125ex]{author in head/foot}%
\usebeamerfont{author in head/foot}\centering\insertshortauthor%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.6\paperwidth,ht=2.5ex,dp=1.125ex]{institute in head/foot}%
\usebeamerfont{institute in head/foot}\centering\insertshorttitle%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.1\paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm ,rightskip=.3cm plus1fil]{title in head/foot}%
\usebeamerfont{title in head/foot}\hfill\insertframenumber/\inserttotalframenumber%
\end{beamercolorbox}}%
\vskip0pt%
}%


\makeatletter
\newcount\beamer@sectionstartframe
\beamer@sectionstartframe=1
\apptocmd{\beamer@section}{\addtocontents{nav}{\protect\headcommand{%
            \protect\beamer@sectionframes{\the\beamer@sectionstartframe}{\the\c@framenumber}}}}{}{}
\apptocmd{\beamer@section}{\beamer@sectionstartframe=\c@framenumber\advance\beamer@sectionstartframe by1\relax}{}{}
\AtEndDocument{\immediate\write\@auxout{\string\@writefile{nav}%
        {\noexpand\headcommand{\noexpand\beamer@sectionframes{\the\beamer@sectionstartframe}{\the\c@framenumber}}}}}{}{}
\def\beamer@startframeofsection{1}
\def\beamer@endframeofsection{1}
\def\beamer@sectionframes#1#2{%
    \ifnum\c@framenumber<#1%
    \else%
    \ifnum\c@framenumber>#2%
    \else%
    \gdef\beamer@startframeofsection{#1}%
    \gdef\beamer@endframeofsection{#2}%
    \fi%
    \fi%
}
\newcommand\insertsectionstartframe{\beamer@startframeofsection}
\newcommand\insertsectionendframe{\beamer@endframeofsection}
\makeatother

\usepackage{tikz}
\usetikzlibrary{calc}

\def\inserttotalsectionframenumber{%
    \pgfmathparse{(\insertsectionendframe-\insertsectionstartframe+1)}%
    \pgfmathprintnumber[fixed,precision=2]{\pgfmathresult}%
}

\def\insertsectionframenumber{%
    \pgfmathparse{(\insertframenumber-\insertsectionstartframe+1)}%
    \pgfmathprintnumber[fixed,precision=2]{\pgfmathresult}%
}

\defbeamertemplate{footline}{page number appendix}
{
\leavevmode%
\hbox{\begin{beamercolorbox}[wd=.3\paperwidth,ht=2.5ex,dp=1.125ex]{author in head/foot}%
\usebeamerfont{author in head/foot}\centering\insertshortauthor%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.6\paperwidth,ht=2.5ex,dp=1.125ex]{institute in head/foot}%
\usebeamerfont{institute in head/foot}\centering\insertshorttitle%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.1\paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm ,rightskip=.3cm plus1fil]{title in head/foot}%
\usebeamerfont{title in head/foot}\hfill%
\insertsectionframenumber/\inserttotalsectionframenumber
\end{beamercolorbox}}%
\vskip0pt%
}

\makeatletter
\g@addto@macro\appendix{%
    \setbeamertemplate{footline}[page number appendix]%
}
\makeatother


\begin{document}
\begin{frame}
Content 1
\end{frame}
\begin{frame}
Content 2
\end{frame}
\begin{frame}
Content 3
\end{frame}
\begin{frame}
Content 3
\end{frame}
\appendix
\section[]{add. Content 1}
\begin{frame}
additional material for content 1
\end{frame}
\begin{frame}
additional material for content 1
\end{frame}
\begin{frame}
additional material for content 1
\end{frame}
\section[]{add. Content 2}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\begin{frame}
additional material for content 2
\end{frame}
\end{document}