Remember when exporting to pdf, a latex file is generated which is then compiled to pdf. You can always look at the generated tex file and try to tweak it. Here, when exporting to pdf, the generated latex file looks ok, but compiling it, through producing a pdf, raises an error. I tracked it down to the fact that \usepackage{metre}
should appear before the \usepackage{amsmath}
inserted by the exporter. I'm not sure how to fix this in org (maybe with the variable org-latex-packages-alist
) but fixing this in the latex file, while removing the error, does not change the output.
Actually, even when compiling the minimal latex file below, the output is still the same. This does not seem to be a problem with emacs or org. I would suggest asking on tex.stackexchange.com.
\documentclass[11pt]{article}
\usepackage[en]{metre}
\begin{document}
\metra{\m\b}
\end{document}