Beamer change frametitle font size just for one slide

Question

I have a slide with long frame title so I want to make the font size smaller. The others are fine so I don't want to change the default settings.

Any ideas how to do it?

Answer 1

The {} will ensure, that the change is only done for the slides within the {}.

\documentclass{beamer}

\begin{document}

    \begin{frame}
        \frametitle{normal title}
        abc
    \end{frame} 

{   
    \setbeamerfont{frametitle}{size=\small}
    \begin{frame}
        \frametitle{extra extra extraextra extra extraextra extra extra extra extra extra long title}
        abc
    \end{frame}         
}

    \begin{frame}
        \frametitle{normal title}
        abc
    \end{frame} 

\end{document}

Answer 2

Samcarter's answer is correct as long as the ignorenonframetext class option is not selected. If it is, the { and } around the slide that was intended to be changed are not noticed. This means the \setbeamerfont command is not localized, and all subsequent slides will have the new (smaller) font size set.

To work around this, make sure there is a group around the slide:

\documentclass[ingorenonframetext]{beamer}

\begin{document}

\begin{frame}
    \frametitle{normal title}
    abc
\end{frame} 

\mode<presentation>{\bgroup}
\setbeamerfont{frametitle}{size=\small}
\begin{frame}
    \frametitle{extra extra extraextra extra extraextra extra extra extra extra extra long title}
    abc
\end{frame}         
\mode<presentation>{\egroup}


\begin{frame}
    \frametitle{normal title}
    abc
\end{frame} 

\end{document}