Source

File: wp-includes/media-template.php

function wp_underscore_audio_template() {
	$audio_types = wp_get_audio_extensions();
	?>
<audio style="visibility: hidden"
	controls
	class="wp-audio-shortcode"
	width="{{ _.isUndefined( data.model.width ) ? 400 : data.model.width }}"
	preload="{{ _.isUndefined( data.model.preload ) ? 'none' : data.model.preload }}"
	<#
	<?php
	foreach ( array( 'autoplay', 'loop' ) as $attr ) :
		?>
	if ( ! _.isUndefined( data.model.<?php echo $attr; ?> ) && data.model.<?php echo $attr; ?> ) {
		#> <?php echo $attr; ?><#
	}
	<?php endforeach ?>#>
>
	<# if ( ! _.isEmpty( data.model.src ) ) { #>
	<source src="{{ data.model.src }}" type="{{ wp.media.view.settings.embedMimes[ data.model.src.split('.').pop() ] }}" />
	<# } #>

	<?php
	foreach ( $audio_types as $type ) :
		?>
	<# if ( ! _.isEmpty( data.model.<?php echo $type; ?> ) ) { #>
	<source src="{{ data.model.<?php echo $type; ?> }}" type="{{ wp.media.view.settings.embedMimes[ '<?php echo $type; ?>' ] }}" />
	<# } #>
		<?php
	endforeach;
	?>
</audio>
	<?php
}