Cropping standalone documents using the beamer option

Question

I have a beamer presentation in which a figure takes a bit long to compile. And I do not want to use externalize. Figures in non-beamer documents can be conveniently produced with standalone. However, if one uses the beamer option there, as is explained in the manual, the figure won't get cropped. Here is my MWE:

\documentclass[beamer]{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{frame}[plain]
\begin{tikzpicture}[xscale=-1,yscale=0.5]
\begin{axis}[hide axis,width=8cm,height=4cm,clip=false] 
\addplot[domain=20:300,samples=800,        
colormap={}{ 
            color(2cm)=(red);
            color(16cm)=(blue);
        },
        ultra thick, point meta=x*x,mesh]{sin(pow(x,2)/15)};
\end{axis}
\node at (-0.2,1) {observer};
\node at (7,1) {source};
\end{tikzpicture}
\end{frame}
\end{document}

Is there a way to persuade standalone to crop the document, or is there an alternative that allows one to achieve this.

NOTE: I was told by samcarter that one could achieve this by changing the font. I agree that this would allow me solve the issue in the present example, but I'd would like to have a general solution. (And no externalize.)

Answer 1

Using the beamer option normally also sets preview=false,crop=false,varwidth=false. The crop=false key can be reverted by passing it as an additional argument:

\documentclass[beamer,crop]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{ducks}
\begin{document}
\begin{tikzpicture}[xscale=-1,yscale=0.5]
\begin{axis}[hide axis,width=8cm,height=4cm,clip=false] 
\addplot[domain=20:300,samples=800,        
colormap={}{ 
            color(2cm)=(red);
            color(16cm)=(blue);
        },
        ultra thick, point meta=x*x,mesh]{sin(pow(x,2)/15)};
\end{axis}
\node at (-0.4,0) {observer};
\node at (7,1) {source};

\draw (-0.4,0.5) pic [scale=0.4,duck/glasses] {duck};

\begin{scope}[yscale=-0.6,xscale=-0.3,yshift=-100,xshift=40]
\fill[gray] (-2.9466,-0.3003) -- (-3.1837,0.4402) -- (-2.7744,0.5708) -- (-2.7308,0.4348) -- (-1.8176,0.7262) -- (-2.6937,2.5325) -- (-2.4891,2.6173) -- (-1.7766,1.1484) -- (-1.7910,2.8438) -- (-1.5698,2.8326) -- (-1.5560,1.2208) -- (-0.8785,2.6173) -- (-0.6739,2.5325) -- (-1.5011,0.8272) -- (-0.3532,1.1935) -- (-0.3096,1.0574) -- (-0.1147,1.1196) -- (-0.0566,0.9382) -- (-0.2516,0.8760) -- (-0.2032,0.7249) -- (-2.5809,-0.0337) -- (-2.5373,-0.1697) -- (-2.9466,-0.3003) -- cycle;
\end{scope}
\end{tikzpicture}
\end{document}