Beamer, frame title and subtitle

Question

I like to have in frame with option \allowframebreaks different \framesubtitle. Solution provided by samcarter_is_at_topanswers.xyz in change-frame-subtitle-after-a-framebreak fulfil this my wish, however I like to change a way of numbering of frames. Instead of \Roman numbers i like to have \arabic numbered on the following way

    (<frame number>/<number of slides in frame>)

which in the case when frame has three slides, are numbered as (1/3), (2/3) and (3/3). How to achieve this?

Code in given link is:

\documentclass{beamer}
\makeatletter
\newcommand*{\slideinframe}{\number\beamer@slideinframe}
\newcounter{bar}
\newcommand{\foo}{%
  \setcounter{bar}{\insertframeendpage}%
  \addtocounter{bar}{-\insertframestartpage}%
  \addtocounter{bar}{1}%
  (\slideinframe/\thebar)%
}
\makeatother
\usepackage{lipsum}
\begin{document}
    \begin{frame}%[allowframebreaks]
        \frametitle{Foo \foo}
        \only<+>{
            \framesubtitle{Bar}
        }
\lipsum[1]
%\framebreak
        \only<+>{
            \framesubtitle{Baz}
        }
\color{red}\lipsum[2]
    \end{frame}
\end{document}

what it do, but consider solution suggested in @samcarter_is_at_topanswers.xyz answer frame is not divided on slides:

But when I uncomment lines in above MWE, slides appear, but numbering not works anymore as expected...

Answer 1

You could calculate the total number of slides within the frame from the start and end pages of the frame:

\documentclass{beamer}
\makeatletter
\newcommand*{\slideinframe}{\number\beamer@slideinframe}
\newcounter{bar}
\newcommand{\foo}{%
  \setcounter{bar}{\insertframeendpage}%
  \addtocounter{bar}{-\insertframestartpage}%
  \addtocounter{bar}{1}%
  (\slideinframe/\thebar)%
}
\makeatother
\usepackage{lipsum}
\begin{document}
    \begin{frame}
        \frametitle{Foo \foo}
        \only<+>{
            \framesubtitle{Bar}
            \lipsum[1]
        }
        \only<+>{
            \framesubtitle{Baz}
            \color{red}\lipsum[2]
        }
    \end{frame}
\end{document}