Adding one more information in my front page - beamer

You can use a line break in author field and add the second line.

\documentclass{beamer}
\usetheme{CambridgeUS} % theme
\title[Project's name]{Project 's name }
\author[My name]{\textbf {Directed by: my name\\ \footnotesize Supervised by: first name, second name}} % auteur
\institute[Rouen University]{\textbf {Rouen University}}
\date{20 july 2012}
\titlegraphic{\includegraphics[width=2cm]{example-image}}
\begin{document}

\begin{frame}
\maketitle
\end{frame}
\end{document}