Auto-populate the frame titles from subsection titles

Is there a way to make `\frametitle` automatically take the `\subsection` heading?

Or maybe equivalently, is there a way to make the section\subsection titles in the header larger? I am afraid the audience may not follow the section\subsection title.

Thanks! (FWIW, so far I've been using the Warsaw theme)

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``````\addtobeamertemplate{frametitle}{\let\insertframetitle\insertsubsectionhead}{}
``````

will replace all frame titles, as far as they exist, but will not magically make a frame title appear if you don't give the argument to the frame environment or give a \frametitle{} command.

``````\makeatletter
\CheckCommand*\beamer@checkframetitle{\@ifnextchar\bgroup\beamer@inlineframetitle{}}
\renewcommand*\beamer@checkframetitle{\global\let\beamer@frametitle\relax\@ifnextchar\bgroup\beamer@inlineframetitle{}}
\makeatother
``````

makes every frame have a title, even if it is \relax by default. (This is somewhat hackish.)

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