This can be done by redefining some of quotchap's internal macros. (Note that my solution somewhat increases the vertical space required by the chapter heading.)
\documentclass{book}
\usepackage{quotchap}
\makeatletter
\renewcommand\chapter{%
\if@openright\cleardoublepage\else\clearpage\fi
\thispagestyle{plain}%
\global\@topnum\z@
% \@printcites% DELETED
\null\hfill\@printcites\par% NEW
\@afterindentfalse
\secdef\@chapter\@schapter
}
\renewcommand{\@makechapterhead}[1]{%
\chapterheadstartvskip%
% {\size@chapter{\sectfont\raggedleft% DELETED
{\size@chapter{\sectfont\raggedright% NEW
{\chapnumfont
\ifnum \c@secnumdepth >\m@ne%
\if@mainmatter\thechapter%
\fi\fi
\par\nobreak}%
% {\raggedleft\advance\leftmargin10em\interlinepenalty\@M #1\par}}% DELETED
{\raggedright\advance\leftmargin10em\interlinepenalty\@M #1\par}}% NEW
\nobreak\chapterheadendvskip}}
\makeatother
\begin{document}
\begin{savequote}[5cm]
A quote.
\qauthor{The author}
\end{savequote}
\chapter{foo}
Some text.
\end{document}
If you have a title on each frame, your generic structure would probably resemble
\begin{frame}
\frametitle{<title>}
% <frame content>
\end{frame}
As such, you have the \frametitle command as a hook that you can use to initiate a different line spacing for the remainder of the frame. And, instead of using the traditional \linespread{<factor>} to modify the spacing, use \setstretch{<factor>} from the setspace package. To that end, include the following in your preamble:
\usepackage{setspace}% http://ctan.org/pkg/setspace
\let\oldframetitle\frametitle% Store \frametitle in \oldframetitle
\renewcommand{\frametitle}[1]{%
\oldframetitle{#1}\setstretch{2}}
This will typeset the regular \frametitle and immediately after it call \setstretch{2} which increases ("doubles") the line spacing for the remainder of the group. Since the frame environment provides the necessary scope boundary, \setstretch only has an effect until \end{frame}. This allows for only the frame content to be typeset under a different line spacing, leaving titles untouched in terms of this stretch factor. Additionally, a natural form of automation by redefinition of the existing commands allow for legible and transferable code.
Here's a minimal example showing this:
\documentclass{beamer}% http://ctan.org/pkg/beamer
\useoutertheme{infolines}
\usetheme{Warsaw}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{setspace}% http://ctan.org/pkg/setspace
\let\oldframetitle\frametitle% Store old \frametitle in \oldframetitle
\renewcommand{\frametitle}[1]{% Redefine \frametitle
\oldframetitle{#1}\setstretch{2}}
%\setstretch{2} <--- uncomment to see the global effect of \setstretch{2}
\title{Random title}
\subtitle{Random subtitle}
\author{Random Randofsky}
\institute{Random institute, Random City 1000, Randomia}
\date{\today}
\begin{document}
\maketitle
\begin{frame}
\tableofcontents
\end{frame}
\section{Random section 1}
\begin{frame}
\frametitle{This frame title is extremely long and spans at least two lines}
\begin{itemize}
\item Random stuff Random stuff
\item \itshape{more random stuff}
\item Random stuff...
\end{itemize}
\end{frame}
\section{Random section 2}
\begin{frame}
\frametitle{Here is another long frame title - this time it spans more than
just two lines of the frame; it actually spans three lines}
\lipsum[4]
\end{frame}
\section{Random section 3}
\begin{frame}
This frame has no title. So, the contents is not affected by line spacing changes
\begin{itemize}
\item Random stuff Random stuff
\item \itshape{more random stuff}
\item Random stuff...
\end{itemize}
\end{frame}
\section{Random section 4}
\begin{frame}
\frametitle{About this frame}
\begin{itemize}
\item Random stuff Random stuff
\item \itshape{more random stuff}
\item Random stuff...
\end{itemize}
\end{frame}
\end{document}
Of course, this relies on the fact that your frame has the structure suggested at the start. So, a frame without a title would be void of any line spacing alterations. Since you didn't mention this in your question, I assume this is not a problem. However, such modifications are always possible, given an alternative/suitable hook.
The lipsum package was merely used to provide filler text on slide 4.
To see the global effect of \setspace{2} on the frame titles, uncomment \setspace{2} in the preamble.
Best Answer
You could use the optional ToC argument of
\chapterand modify the mandatory argument using\setstretchfromsetspace. Here's a minimal example showing the difference in output:You can't just use the mandatory argument to manage the line spread since it makes its way into the ToC without an optional argument.