Sort media by rtMedia custom attributes

functions.php

<?php
/**
 * This code snippet enhances the sort functionality provided by rtMedia Sorting plugin by providing sorting using
 * custom attributes that is created by rtMedia Custom Attributes plugin.
 * Both rtMedia Custom Attributes and rtMedia Sorting plugins must be enabled for this code snippet to work.
 */

// Enter attribute slug here.
$rtm_attributes_slug = 'camera';

// Enter term slug here.
$rtm_term_slug = array(
	'canon',
	'nikon',
);

if ( is_plugin_active( 'rtmedia-custom-attributes/index.php' ) && is_plugin_active( 'rtmedia-sorting/index.php' ) ) {

	$tmp_rtm_add_attributes_cb = function() use ( $rtm_attributes_slug, $rtm_term_slug ) {

		$tmp_rtm_attr_model = new RTMediaAttributesModel();
		$attribute_label = $tmp_rtm_attr_model->get_attribute_label( $rtm_attributes_slug );

		if ( ! empty( $attribute_label ) ) {

			$taxonomy_name = rtmedia_attribute_taxonomy_name( $rtm_attributes_slug );
			$terms = get_terms( array(
				'taxonomy'	=> $taxonomy_name,
			) );

			foreach ( $terms as $term ) {

				if ( in_array( $term->slug, $rtm_term_slug, true ) ) {

					$tmp_rtm_change_sort_parameter_cb = function( $rtmedia_sort_labels ) use ( $term ) {
						$rtmedia_sort_labels[ $term->slug ] = $term->name;
						return $rtmedia_sort_labels;
					};
					add_filter( 'rtmedia_change_sort_parameters_label', $tmp_rtm_change_sort_parameter_cb, 99 );

					$tmp_rtm_media_query_cb = function( $media_query ) use ( $term ) {
						if ( ! empty( $media_query['sort_parameters'] ) ) {
							$media_query['sort_parameters'] .= ',' . $term->slug;
						}
						return $media_query;
					};
					add_filter( 'rtmedia_media_query', $tmp_rtm_media_query_cb, 9 );


					$tmp_rtm_query_filter_cb = function( $args ) use ( $term, $taxonomy_name ) {

						$data = wp_unslash( $_GET ); // Input var okay.
						if ( ! empty( sanitize_text_field( $data['json'] ) ) ) {
							if ( ! empty( sanitize_text_field( $data['sort_by'] ) ) ) {
								switch ( sanitize_text_field( $data['sort_by'] ) ) {
									case $term->slug :
										$args['order_by'] = 'media_id';

										$tmp_rtm_model_join_query_cb = function( $join, $table_name ) use ( $term, $taxonomy_name ) {

											$join .= "JOIN wp_term_relationships 
												ON wp_term_relationships.object_id = {$table_name}.media_id
												JOIN wp_term_taxonomy
												ON wp_term_taxonomy.term_taxonomy_id = wp_term_relationships.term_taxonomy_id AND wp_term_taxonomy.taxonomy = '" . $taxonomy_name . "'
												JOIN wp_terms
												ON wp_terms.term_id = wp_term_taxonomy.term_id AND wp_terms.slug = '" . $term->slug . "'";

											return $join;

										};
										add_filter( 'rtmedia-model-join-query', $tmp_rtm_model_join_query_cb, 99, 2 );

										break;
								}
							}

							if ( ! empty( sanitize_text_field( $data['sort_order'] ) ) ) {
								switch ( sanitize_text_field( $data['sort_order'] ) ) {
									case 'asc' :
										$args['order'] = 'ASC';
										break;

									default :
										$args['order'] = 'DESC';
										break;
								}
							}
						} // End if().

						return $args;

					};
					add_filter( 'rtmedia_query_filter', $tmp_rtm_query_filter_cb, 99 );

				} // End if().
			} // End foreach().
		} // End if().
	};

	add_action( 'init', $tmp_rtm_add_attributes_cb, 99 );

} // End if().

Add the above code to your theme's functions.php file.

Change $rtm_attributes_slug and $rtm_term_slug variable as per your requirement.

Example:
As described here, if you want to have macro and prime term of lens attribute as a sorting parameter,
change top of the code like below:

// Enter attribute slug here.
$rtm_attributes_slug = 'lens';

// Enter term slug here.
$rtm_term_slug = array(
	'macro',
	'prime',
);

If you want to pre-sort the media using custom attributes, you can use the below shortcode:
[rtmedia_gallery attribute_slug="lens" term_slug="macro, prime"]