Unwanted vertical shift on figure when replacing itemize

Question

So, I spend like few hours trying to fix my problem. I've got an image that I want to stay at the SAME position during all the slide. And on other side, I want a list of item with overlay/replacing tricks.

To do that, I used this code (by the way, the itemize with only isn't optimize at all, but I want to replace previous item, so I don't know how to do it in one line):

\documentclass[hyperref={pdfpagemode=FullScreen},xcolor=table,t]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{mwe}

\begin{document}
\begin{frame}
\frametitle{Frame Title}
\begin{minipage}[c]{0.24\textwidth}
    \includegraphics[width=\textwidth]{example-image}
\end{minipage}
\hfill
\begin{minipage}[c]{0.74\textwidth}
\includegraphics<1-2>[width=\textwidth]{example-image-a}
\includegraphics<3>[width=\textwidth]{example-image-b}
\only<1>{
\begin{itemize}
    \item blablabla
\end{itemize}
}
\only<2>{
\begin{itemize}
    \item blablabla
    \item blablabla
\end{itemize}
}
\only<3>{
\begin{itemize}
    \item blablabla
\end{itemize}
}
\end{minipage}
\end{frame}
\end{document}

As you can see there, the image on the left is moving vertically. But why ? Image is moving with the item apparition... How to deal with the apparitions without moving the image ?

Answer 1

Just to understand where your problem comes from, you could imagine the minipages as boxes. In your example they behave like this:

---

I would suggest columns instead of ordinary minipages. The main advantage is that they allow you to specify a top alignment across the columns which will allow a stable positions despite the fact that the second column changes height between the slides.

Alternatively you could use an overlayarea, but I think using columns is easier.

Unrelated to the problem: instead of replacing the whole itemize environment, you could just pass the overlay instructions to the individual items.

\documentclass[t]{beamer}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
%\usepackage{mwe}

\begin{document}
\begin{frame}
\frametitle{Frame Title}
\begin{columns}[T,onlytextwidth]
\begin{column}{.24\textwidth}
    \vspace*{3cm}
    \includegraphics[width=\textwidth]{example-image}
\end{column}
\begin{column}{.74\textwidth}
    \includegraphics<1-2>[width=\textwidth]{example-image-a}
    \includegraphics<3>[width=\textwidth]{example-image-b}
    \begin{itemize}
        \item<only@1> blablabla1
        \item<only@2> blablabla2a
        \item<only@2> blablabla2b
        \item<only@3> blablabla3
    \end{itemize}
\end{column}
\end{columns}
\end{frame}
\end{document}