How to fix the postion of blocks while changing images in beamer presentation?

Question

I would like to make an animation using beamer. A picture should replace another during the transition. I have a problem that the text will move its position during this animation. I have tried \only and \onslide but the question is not solved.

\begin{frame}{}
\onslide<1->{some text }
 \onlide<1>{
 \begin{figure}[H]
  \centering
  \includegraphics[width=4in]{Figures/fig1.pdf}
\label{fig2}
\end{figure}
}
\onslide<2->{
\begin{figure}[H]
  \centering
  \includegraphics[,width=4in]{Figures/fig2.pdf}
\label{fig2}
\end{figure}
}


\end{frame}

The position of "some text" moves during animation.

Answer 1

• your code has many unprotected line endings (missing % at the end of lines) that act like a space

• onlide should be onslide

• \onslide<> makes the content just invisible, but still reserves space. You want to use \only instead

• floating specifier such as [H] don't make sense in a documentclass without floating mechanism

• \centering is unnecessary, beamer figures are centred by default

• you must not use the same lable multiple times

• \includeggraphics is overlay aware, just use that and avoid all the other pitfalls:

\documentclass{beamer}

\begin{document}
    
\begin{frame}
\begin{figure}
  \includegraphics<+>[width=4in]{example-image}
  \includegraphics<+>[width=4in]{example-image-duck}
\end{figure}
\end{frame} 
    
\end{document}