by

< ?php

add_filter( 'upload_mimes', 'ar_add_flac_support' );
/**
 * Introduces functionality that allows us to upload Flac files which are not
 * supported by the enc_type="multipart/form-data" attribute.
 *
 * @param  array $mimes The current array of MIME types that are supported.
 * @return array $mimes The updated array of supported MIME types.
 */
function ar_add_flac_support( $mimes ) {

    $mimes = array_merge(
        $mimes,
        array(
            'flac' => 'application/x-flac',
        )
    );

    return $mimes;

}