I’ve also tried this:
//Add Audio to Podcast Feed
function add_audio_to_feed($content) {
if(is_feed()) {
$post_id = get_the_ID();
$output .= '<audio controls> <source src="' . the_field('podcast') . '" type="audio/mpeg"></audio>';
$content = $content.$output;
}
return $content;
}
add_filter('the_content','add_audio_to_feed');