MyPlugin.pm

sub register( $self, $site ) {
    $site->on( build => sub( $event ) {
        for my $page ( $event->pages->@* ) {
            $page->dom->find( 'img[src$=.mp3]' )->each( sub( $el ) {
                $el->replace( '<audio controls><source type="audio/mp3" src="%s"></audio>', $el->attr( 'src' ) );
            } );
        }
    } );
}