Issue #2969691 by thejacer87, matthieuscarset, lhangea, rwohleb, alexpott: Muted attribute not working for Video file

core/modules/file/src/Plugin/Field/FieldFormatter/FileMediaFormatterBase.php

@@ -151,7 +151,7 @@ abstract class FileMediaFormatterBase extends FileFormatterBase implements FileM
    */
   protected function prepareAttributes(array $additional_attributes = []) {
     $attributes = new Attribute();
-    foreach (['controls', 'autoplay', 'loop'] + $additional_attributes as $attribute) {
+    foreach (array_merge(['controls', 'autoplay', 'loop'], $additional_attributes) as $attribute) {
       if ($this->getSetting($attribute)) {
         $attributes->setAttribute($attribute, $attribute);
       }

core/modules/file/tests/src/Functional/Formatter/FileVideoFormatterTest.php

@@ -55,4 +55,44 @@ class FileVideoFormatterTest extends FileMediaFormatterTestBase {
     $assert_session->elementExists('css', "video > source[src='$file2_url'][type='video/mp4']");
   }
 
+  /**
+   * Tests that the attributes added to the formatter are applied on render.
+   */
+  public function testAttributes() {
+    $field_config = $this->createMediaField(
+      'file_video',
+      'mp4',
+      [
+        'autoplay' => TRUE,
+        'loop' => TRUE,
+        'muted' => TRUE,
+      ]
+    );
+
+    file_put_contents('public://file.mp4', str_repeat('t', 10));
+    $file = File::create([
+      'uri' => 'public://file.mp4',
+      'filename' => 'file.mp4',
+    ]);
+    $file->save();
+
+    $entity = EntityTest::create([
+      $field_config->getName() => [
+        [
+          'target_id' => $file->id(),
+        ],
+      ],
+    ]);
+    $entity->save();
+
+    $this->drupalGet($entity->toUrl());
+
+    $file_url = file_url_transform_relative(file_create_url($file->getFileUri()));
+
+    $assert_session = $this->assertSession();
+    $assert_session->elementExists('css', "video[autoplay='autoplay'] > source[src='$file_url'][type='video/mp4']");
+    $assert_session->elementExists('css', "video[loop='loop'] > source[src='$file_url'][type='video/mp4']");
+    $assert_session->elementExists('css', "video[muted='muted'] > source[src='$file_url'][type='video/mp4']");
+  }
+
 }