Media: Add an opt-in filter to generate animated image sub-sizes

src/wp-admin/edit-form-blocks.php

@@ -89,6 +89,7 @@ static function ( $classes ) {
 	'/?_fields=' . implode(
 		',',
 		array(
+			'animated_image_subsizes',
 			'description',
 			'gmt_offset',
 			'home',

src/wp-admin/site-editor.php

@@ -215,6 +215,7 @@ static function ( $classes ) {
 	'/?_fields=' . implode(
 		',',
 		array(
+			'animated_image_subsizes',
 			'description',
 			'gmt_offset',
 			'home',

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -1378,6 +1378,27 @@ public function get_index( $request ) {
 
 			/** This filter is documented in wp-admin/includes/image.php */
 			$available['image_size_threshold'] = (int) apply_filters( 'big_image_size_threshold', 2560, array( 0, 0 ), '', 0 );
+
+			/**
+			 * Filters whether sub-sizes of animated images should keep their animation.
+			 *
+			 * By default, sub-sizes of animated images (e.g. animated GIFs) are static,
+			 * generated from the first frame only. Re-encoding every frame per sub-size
+			 * is very resource intensive, so animated sub-sizes are opt-in.
+			 *
+			 * This currently only affects the client-side media processing path,
+			 * where all frames can be decoded and re-encoded in the browser. Only
+			 * uncropped sub-sizes keep their animation; cropped sizes (such as
+			 * `thumbnail`) are always generated from the first frame. Uploads that
+			 * take the server-side path also still produce static sub-sizes, as
+			 * neither GD nor Imagick resizing preserves animation in core.
+			 *
+			 * @since 7.2.0
+			 *
+			 * @param bool $animated_image_subsizes Whether to generate animated sub-sizes
+			 *                                      for animated images. Default false.
+			 */
+			$available['animated_image_subsizes'] = (bool) apply_filters( 'wp_generate_animated_image_subsizes', false );
 		}
 
 		$response = new WP_REST_Response( $available );

tests/phpunit/tests/rest-api/rest-server.php

@@ -1207,6 +1207,64 @@ public function test_get_index() {
 		$this->assertArrayHasKey( 'site_icon_url', $data );
 	}
 
+	/**
+	 * @ticket 65656
+	 *
+	 * @covers WP_REST_Server::get_index
+	 */
+	public function test_get_index_should_include_animated_image_subsizes(): void {
+		$user_id = self::factory()->user->create( array( 'role' => 'administrator' ) );
+		$this->assertIsInt( $user_id );
+		wp_set_current_user( $user_id );
+		add_filter( 'wp_client_side_media_processing_enabled', '__return_true' );
+
+		$server  = new WP_REST_Server();
+		$request = new WP_REST_Request( 'GET', '/' );
+		$index   = $server->dispatch( $request );
+		$data    = $index->get_data();
+		$this->assertIsArray( $data );
+
+		$this->assertArrayHasKey( 'animated_image_subsizes', $data );
+		$this->assertFalse( $data['animated_image_subsizes'] );
+	}
+
+	/**
+	 * @ticket 65656
+	 *
+	 * @covers WP_REST_Server::get_index
+	 */
+	public function test_get_index_should_not_include_animated_image_subsizes_without_caps(): void {
+		add_filter( 'wp_client_side_media_processing_enabled', '__return_true' );
+
+		$server  = new WP_REST_Server();
+		$request = new WP_REST_Request( 'GET', '/' );
+		$index   = $server->dispatch( $request );
+		$data    = $index->get_data();
+		$this->assertIsArray( $data );
+
+		$this->assertArrayNotHasKey( 'animated_image_subsizes', $data );
+	}
+
+	/**
+	 * @ticket 65656
+	 *
+	 * @covers WP_REST_Server::get_index
+	 */
+	public function test_get_index_should_honor_animated_image_subsizes_filter(): void {
+		$user_id = self::factory()->user->create( array( 'role' => 'administrator' ) );
+		$this->assertIsInt( $user_id );
+		wp_set_current_user( $user_id );
+		add_filter( 'wp_client_side_media_processing_enabled', '__return_true' );
+		add_filter( 'wp_generate_animated_image_subsizes', '__return_true' );
+
+		$server  = new WP_REST_Server();
+		$request = new WP_REST_Request( 'GET', '/' );
+		$index   = $server->dispatch( $request );
+		$data    = $index->get_data();
+
+		$this->assertTrue( $data['animated_image_subsizes'] );
+	}
+
 	/**
 	 * @ticket 57902
 	 *

tests/qunit/fixtures/wp-api-generated.js

@@ -13061,6 +13061,7 @@ mockedApiResponse.Schema = {
         }
     },
     "image_size_threshold": 2560,
+    "animated_image_subsizes": false,
     "site_logo": 0,
     "site_icon": 0,
     "site_icon_url": ""