reverted:
--- b/core/modules/media/js/ajax.js
+++ /dev/null
@@ -1,32 +0,0 @@
-(function ($, Drupal) {
-
-  'use strict';
-
-  /**
-   * JavaScript handler for opening of modal add media form.
-   *
-   * TODO: es6.js!!!
-   *
-   * @param ajax
-   * @param response
-   * @param status
-   */
-  Drupal.AjaxCommands.prototype.openModalMediaForm = function (ajax, response, status) {
-    var openDialogAjax = new Drupal.Ajax(null, null, {
-      url: '/media/add-modal',
-      dialogType: 'modal',
-      submit: {
-        file_ids: response.file_ids,
-        field_widget_id: response.field_widget_id,
-        dialogOptions: {
-          width: 800
-        }
-      },
-      progress: {
-        type: 'throbber'
-      }
-    });
-
-    openDialogAjax.execute();
-  };
-})(jQuery, Drupal);
reverted:
--- b/core/modules/media/media.libraries.yml
+++ a/core/modules/media/media.libraries.yml
@@ -11,8 +11,3 @@
     js/type_form.js: {}
   dependencies:
     - core/drupal.form
-
-open_modal_media_form:
-  version: VERSION
-  js:
-    js/ajax.js: {}
diff -u b/core/modules/media/media.module b/core/modules/media/media.module
--- b/core/modules/media/media.module
+++ b/core/modules/media/media.module
@@ -110,19 +110,15 @@
  *   Result of validation.
  */
 function media_validate_file_upload(FileInterface $file) {
-  $extension = pathinfo($file->getFilename(), PATHINFO_EXTENSION);
+  $media_types = \Drupal::service('media.type_guesser.file')->getTypesForFile($file);
 
-  $availableMediaTypes = \Drupal::service('media_type.manager')
-    ->getTypesByExtension($extension);
-
-  if (empty($availableMediaTypes)) {
+  if (empty($media_types)) {
     return [
       t('%filename could not be matched to any media types.', [
         '%filename' => $file->getFilename(),
       ]),
     ];
   }
-
   return [];
 }
 
diff -u b/core/modules/media/media.routing.yml b/core/modules/media/media.routing.yml
--- b/core/modules/media/media.routing.yml
+++ b/core/modules/media/media.routing.yml
@@ -20,13 +20,6 @@
     _access_media_revision: 'view'
     media: \d+
 
-entity.media.add_modal:
-  path: '/media/add-modal'
-  defaults:
-    _form: '\Drupal\media\Form\MediaModalForm'
-  requirements:
-    _entity_create_access: media
-
 entity.media.add_file:
   path: '/media/add-file/{media_type}/{file}/{selector}'
   defaults:
reverted:
--- b/core/modules/media/src/Form/MediaModalForm.php
+++ /dev/null
@@ -1,580 +0,0 @@
-<?php
-
-namespace Drupal\media\Form;
-
-use Drupal\Core\Ajax\AjaxResponse;
-use Drupal\Core\Ajax\CloseModalDialogCommand;
-use Drupal\Core\Ajax\ReplaceCommand;
-use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Entity\EntityTypeManagerInterface;
-use Drupal\Core\Form\FormBase;
-use Drupal\Core\Form\FormInterface;
-use Drupal\Core\Form\FormState;
-use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Form\FormSubmitterInterface;
-use Drupal\Core\Form\FormValidatorInterface;
-use Drupal\Core\Render\Element;
-use Drupal\Core\Render\ElementInfoManagerInterface;
-use Drupal\Core\Render\RendererInterface;
-use Drupal\media\Entity\Media;
-use Drupal\media\MediaTypeManagerInterface;
-use Symfony\Component\DependencyInjection\ContainerInterface;
-
-/**
- * Modal form for adding media from uploaded files.
- *
- * TODO:
- *   - IMPORTANT: return 'processed_media_ids' to widget, to display selected
- *     medias.
- *   - sub media form should use different form display mode. Because it should
- *     not be allowed for user to remove file!
- *   - improve error handling (fe. invalid form, no available media type, etc.)
- *   - Additional Refactoring and after that one more refactoring.
- *   - TESTS!!!
- *
- * @package Drupal\media\Form
- */
-class MediaModalForm extends FormBase {
-
-  /**
-   * Key used to store inner form object in outer form state.
-   */
-  const INNER_FORM_OBJECT_KEY = 'inner_form_object';
-
-  /**
-   * Key used to store inner form state in outer form state.
-   */
-  const INNER_FORM_STATE_KEY = 'inner_form_state';
-
-  /**
-   * Inner form ID used in form array.
-   */
-  const INNER_FORM_ID = 'inner_form';
-
-  /**
-   * Renderer service.
-   *
-   * @var \Drupal\Core\Render\RendererInterface
-   */
-  protected $renderer;
-
-  /**
-   * Element info manager service.
-   *
-   * @var \Drupal\Core\Render\ElementInfoManagerInterface
-   */
-  protected $elementInfo;
-
-  /**
-   * Form validator service.
-   *
-   * @var \Drupal\Core\Form\FormValidatorInterface
-   */
-  protected $formValidator;
-
-  /**
-   * Form submitter service.
-   *
-   * @var \Drupal\Core\Form\FormSubmitterInterface
-   */
-  protected $formSubmitter;
-
-  /**
-   * Entity type manager service.
-   *
-   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
-   */
-  protected $entityTypeManager;
-
-  /**
-   * Media type manager.
-   *
-   * @var \Drupal\media\MediaTypeManagerInterface
-   */
-  protected $mediaTypeManager;
-
-  /**
-   * Media modal form constructor.
-   *
-   * @param \Drupal\Core\Render\RendererInterface $renderer
-   *   Renderer service.
-   * @param \Drupal\Core\Render\ElementInfoManagerInterface $element_info
-   *   Element infor manager service.
-   * @param \Drupal\Core\Form\FormValidatorInterface $form_validator
-   *   Form validator service.
-   * @param \Drupal\Core\Form\FormSubmitterInterface $form_submitter
-   *   Form submitter service.
-   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
-   *   Entity type manager service.
-   * @param \Drupal\media\MediaTypeManagerInterface $media_type_manager
-   *   Media type manager service.
-   */
-  public function __construct(RendererInterface $renderer, ElementInfoManagerInterface $element_info, FormValidatorInterface $form_validator, FormSubmitterInterface $form_submitter, EntityTypeManagerInterface $entity_type_manager, MediaTypeManagerInterface $media_type_manager) {
-    $this->renderer = $renderer;
-    $this->elementInfo = $element_info;
-    $this->formValidator = $form_validator;
-    $this->formSubmitter = $form_submitter;
-    $this->entityTypeManager = $entity_type_manager;
-    $this->mediaTypeManager = $media_type_manager;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public static function create(ContainerInterface $container) {
-    return new static(
-      $container->get('renderer'),
-      $container->get('element_info'),
-      $container->get('form_validator'),
-      $container->get('form_submitter'),
-      $container->get('entity_type.manager'),
-      $container->get('media_type.manager')
-    );
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getFormId() {
-    return 'media_modal_form';
-  }
-
-  /**
-   * Init form state, it's executed for first time when dialog is open.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state.
-   */
-  protected function initFormState(FormStateInterface $form_state) {
-    // Get data provided by OpenModalMediaFormCommand.
-    $form_state->set('queued_fids', $form_state->getUserInput()['file_ids']);
-    $form_state->set('field_widget_id', $form_state->getUserInput()['field_widget_id']);
-
-    // Init clean state of processed media IDs.
-    $form_state->set('processed_media_ids', []);
-
-    $form_state->setCached(TRUE);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function buildForm(array $form, FormStateInterface $form_state) {
-    // Initialize form state if there are no queued files.
-    if (empty($form_state->get('queued_fids'))) {
-      $this->initFormState($form_state);
-    }
-
-    // Get file IDs that should be processed.
-    $file_ids = $form_state->get('queued_fids');
-
-    // Get list of available media types for file.
-    $file = $this->getFileById($file_ids[0]);
-    $list_of_media_types = $this->getMediaTypeList($file_ids[0]);
-
-    // Get selected media type.
-    $trigger_element = $form_state->getTriggeringElement();
-    if (!empty($trigger_element) && $trigger_element['#name'] === 'media_type') {
-      $selected_media_type = $trigger_element['#value'];
-    }
-    else {
-      reset($list_of_media_types);
-      $selected_media_type = key($list_of_media_types);
-    }
-
-    // Create media entity from file.
-    $media = $this->createMediaFromFile($selected_media_type, $file);
-
-    // Generate form.
-    $form['#prefix'] = '<div id="media-modal-form">';
-    $form['#suffix'] = '</div>';
-
-    $form['status_messages'] = $this->getStatusMessagesElement($form_state);
-
-    $form['media_type'] = $this->getTypeSelectElement($list_of_media_types);
-
-    // Prepare inner media form.
-    $form['#process'] = $this->elementInfo->getInfoProperty('form', '#process', []);
-    $form['#process'][] = '::processForm';
-    $form[static::INNER_FORM_ID] = $this->getInnerMediaForm($form_state, $media);
-
-    // Create action buttons for modal dialog.
-    $form['actions'] = $this->getActionsElement();
-
-    return $form;
-  }
-
-  /**
-   * Creates build array for media type selector.
-   *
-   * Prefix is required in order to properly replace element over AJAX.
-   *
-   * @param array $list_of_media_types
-   *   List of media types that should be displayed in select field.
-   *
-   * @return array
-   *   Returns build array for media type selector.
-   */
-  protected function getTypeSelectElement(array $list_of_media_types) {
-    return [
-      '#id' => 'media-modal-form-media-type',
-      '#prefix' => '<div id="media-modal-form-media-type-wrapper">',
-      '#suffix' => '</div>',
-      '#type' => 'select',
-      '#title' => $this->t('Media type'),
-      '#options' => $list_of_media_types,
-      '#ajax' => [
-        'callback' => '::ajaxChangeType',
-        'wrapper' => 'media-modal-form',
-      ],
-    ];
-  }
-
-  /**
-   * Get build array for actions element.
-   *
-   * @return array
-   *   Returns actions build array.
-   */
-  protected function getActionsElement() {
-    $actionsElement = [
-      '#type' => 'actions',
-    ];
-
-    $actionsElement['submit_form'] = [
-      '#type' => 'submit',
-      '#name' => 'media-modal-form-submit',
-      '#value' => $this->t('Save'),
-      '#validate' => ['::validateForm'],
-      '#submit' => ['::submitForm'],
-      '#ajax' => [
-        'callback' => '::ajaxSubmitForm',
-        'wrapper' => 'media-modal-form',
-        'event' => 'click',
-      ],
-    ];
-
-    return $actionsElement;
-  }
-
-  /**
-   * Get status messages element.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state.
-   *
-   * @return array
-   *   Returns status messages element.
-   */
-  protected function getStatusMessagesElement(FormStateInterface $form_state) {
-    $status_messages_element = [
-      '#prefix' => '<div id="media-modal-form-status-messages">',
-      '#suffix' => '</div>',
-    ];
-
-    if ($form_state->getErrors()) {
-      $status_messages_element['#type'] = 'status_messages';
-    }
-
-    return $status_messages_element;
-  }
-
-  /**
-   * Generate inner media form for provided media entity.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state.
-   * @param \Drupal\Core\Entity\EntityInterface $media
-   *   Media entity that will be edited in inner form.
-   *
-   * @return array
-   *   Returns render array for inner media form.
-   */
-  protected function getInnerMediaForm(FormStateInterface $form_state, EntityInterface $media) {
-    $inner_form_object = \Drupal::entityTypeManager()
-      ->getFormObject('media', 'edit')
-      ->setEntity($media);
-
-    $form_state->set(static::INNER_FORM_OBJECT_KEY, $inner_form_object);
-
-    $inner_form_state = static::createInnerFormState($form_state, $inner_form_object);
-
-    $inner_form = ['#parents' => [static::INNER_FORM_ID]];
-    $inner_form = $inner_form_object->buildForm($inner_form, $inner_form_state);
-
-    $inner_form['#prefix'] = '<div id="media-modal-form-inner-form">';
-    $inner_form['#suffix'] = '</div>';
-
-    $inner_form['#type'] = 'container';
-    $inner_form['#theme_wrappers'] = $this->elementInfo->getInfoProperty('container', '#theme_wrappers', []);
-    unset($inner_form['form_token']);
-
-    if (!empty($inner_form['#process'])) {
-      $inner_form_state->set('#process', $inner_form['#process']);
-      unset($inner_form['#process']);
-    }
-    else {
-      $inner_form_state->set('#process', []);
-    }
-
-    // Remove actions from subform, because wrapping form will handle it.
-    if (!empty($inner_form['actions'])) {
-      if (isset($inner_form['actions']['submit'])) {
-        $inner_form['#submit'] = $inner_form['actions']['submit']['#submit'];
-      }
-      unset($inner_form['actions']);
-    }
-    $inner_form['#element_validate'][] = '::validateForm';
-
-    return $inner_form;
-  }
-
-  /**
-   * Process inner form.
-   *
-   * @param array $form
-   *   Form array.
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state.
-   * @param array $complete_form
-   *   Complete form.
-   *
-   * @return array
-   *   Returns processed form.
-   */
-  public function processForm(array &$form, FormStateInterface &$form_state, array &$complete_form) {
-    $inner_form_state = static::getInnerFormState($form_state);
-
-    foreach ($inner_form_state->get('#process') as $callback) {
-      $form[static::INNER_FORM_ID] = call_user_func_array($inner_form_state->prepareCallback($callback), array(
-        &$form[static::INNER_FORM_ID],
-        &$inner_form_state,
-        &$complete_form,
-      ));
-    }
-
-    return $form;
-  }
-
-  /**
-   * Creates new inner form state.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state for outer form.
-   * @param \Drupal\Core\Form\FormInterface $inner_form_object
-   *   Inner form object.
-   *
-   * @return \Drupal\Core\Form\FormState
-   *   Returns created inner form state.
-   */
-  protected static function createInnerFormState(FormStateInterface $form_state, FormInterface $inner_form_object) {
-    $inner_form_state = new FormState();
-    $inner_form_state->setFormObject($inner_form_object);
-    $form_state->set([
-      static::INNER_FORM_STATE_KEY,
-      static::INNER_FORM_ID,
-    ], $inner_form_state);
-
-    return $inner_form_state;
-  }
-
-  /**
-   * Get inner form state.
-   *
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Outer form state.
-   *
-   * @return \Drupal\Core\Form\FormStateInterface
-   *   Returns inner form state.
-   */
-  protected static function getInnerFormState(FormStateInterface $form_state) {
-    /** @var \Drupal\Core\Form\FormStateInterface $inner_form_state */
-    $inner_form_state = $form_state->get([
-      static::INNER_FORM_STATE_KEY,
-      static::INNER_FORM_ID,
-    ]);
-
-    $inner_form_state->setCompleteForm($form_state->getCompleteForm());
-    $inner_form_state->setValues($form_state->getValues() ?: []);
-    $inner_form_state->setUserInput($form_state->getUserInput() ?: []);
-
-    return $inner_form_state;
-  }
-
-  /**
-   * Create media entity for file.
-   *
-   * @param string $type
-   *   Media type.
-   * @param \Drupal\Core\Entity\EntityInterface $file
-   *   File entity that will be used to create media entity.
-   *
-   * @return \Drupal\Core\Entity\EntityInterface
-   *   Returns media entity.
-   */
-  protected function createMediaFromFile($type, EntityInterface $file) {
-    $media_item = Media::create([
-      'bundle' => $type,
-    ]);
-
-    $configuration = $media_item->getSource()->getConfiguration();
-    $media_item->set($configuration['source_field'], $file);
-
-    return $media_item;
-  }
-
-  /**
-   * Get file entity for file ID.
-   *
-   * @param string $file_id
-   *   File ID.
-   *
-   * @return \Drupal\Core\Entity\EntityInterface
-   *   Returns file entity.
-   */
-  protected function getFileById($file_id) {
-    /** @var \Drupal\file\FileStorage $file_storage */
-    $file_storage = \Drupal::service('entity_type.manager')->getStorage('file');
-
-    return $file_storage->load($file_id);
-  }
-
-  /**
-   * Get media type list.
-   *
-   * @param string $file_id
-   *   File ID.
-   *
-   * @return array
-   *   Returns available list of media types for file extension.
-   */
-  protected function getMediaTypeList($file_id) {
-    /** @var \Drupal\file\FileInterface $file */
-    $file = $this->getFileById($file_id);
-
-    $extension = pathinfo($file->getFilename(), PATHINFO_EXTENSION);
-
-    return $this->mediaTypeManager->getTypesByExtension($extension);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function validateForm(array &$form, FormStateInterface $form_state) {
-    // Validate form only if submit button triggers AJAX request.
-    if ($form_state->getTriggeringElement()['#name'] === 'media-modal-form-submit') {
-      $inner_form_object = $form_state->get(static::INNER_FORM_OBJECT_KEY);
-      $inner_form_state = static::getInnerFormState($form_state);
-
-      // Clear status of inner form state.
-      $form_state->clearErrors();
-      $inner_form_state->clearErrors();
-      $inner_form_state->setValidationComplete(FALSE);
-
-      // Pass through both the form elements validation and the form object
-      // validation.
-      $inner_form_id = $inner_form_object->getFormId();
-      $this->invalidateInnerForm($form[static::INNER_FORM_ID]);
-      $inner_form_state->setUserInput($form_state->getUserInput()[static::INNER_FORM_ID]);
-      $inner_form_state->setValues($form_state->getValue(static::INNER_FORM_ID));
-      $this->formValidator->validateForm($inner_form_id, $form[static::INNER_FORM_ID], $inner_form_state);
-
-      foreach ($inner_form_state->getErrors() as $error_element_path => $error) {
-        // TODO: should be improved for inline error message to work.
-        $form_state->setErrorByName(static::INNER_FORM_ID . '][' . $error_element_path, $error);
-      }
-    }
-  }
-
-  protected function invalidateInnerForm(array &$elements) {
-    unset($elements['#validated']);
-
-    foreach (Element::children($elements) as $key) {
-      if (is_array($elements[$key])) {
-        $this->invalidateInnerForm($elements[$key]);
-      }
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function submitForm(array &$form, FormStateInterface $form_state) {
-    $inner_form_state = static::getInnerFormState($form_state);
-    $inner_form_state->setSubmitted();
-    $this->formSubmitter->doSubmitForm($form[static::INNER_FORM_ID], $inner_form_state);
-
-    $file_ids = $form_state->get('queued_fids');
-    array_shift($file_ids);
-    $form_state->set('queued_fids', $file_ids);
-
-    $processed_ids = $form_state->get('processed_media_ids');
-    $processed_ids[] = $form_state->get(static::INNER_FORM_OBJECT_KEY)
-      ->getEntity()
-      ->id();
-    $form_state->set('processed_media_ids', $processed_ids);
-
-    if (!empty($file_ids)) {
-      $form_state->setRebuild();
-    }
-  }
-
-  /**
-   * AJAX response after submitting of form.
-   *
-   * It can go in two directions:
-   *   - when last file is processed dialog will be closed and created media IDs
-   *     passed to caller component.
-   *   - if there are more queued files, next file will be displayed in form.
-   *
-   * @param array $form
-   *   Form array.
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state.
-   *
-   * @return \Drupal\Core\Ajax\AjaxResponse
-   *   Returns AJAX response.
-   */
-  public function ajaxSubmitForm(array &$form, FormStateInterface $form_state) {
-    $fileIds = $form_state->get('queued_fids');
-
-    // All files are processed, close dialog and send information to caller.
-    if (empty($fileIds)) {
-      $response = new AjaxResponse();
-
-      // TODO: Add exeuction of JS Command that will send processed media IDs to
-      // widget.
-      $response->addCommand(new CloseModalDialogCommand());
-    }
-    else {
-      $response = $this->ajaxChangeType($form, $form_state);
-
-      $selection_button_html = trim($this->renderer->renderRoot($form['media_type']));
-      $response->addCommand(new ReplaceCommand('#media-modal-form-media-type-wrapper', $selection_button_html));
-      $response->addCommand(new ReplaceCommand('#media-modal-form-status-messages', $this->getStatusMessagesElement($form_state)));
-    }
-
-    return $response;
-  }
-
-  /**
-   * AJAX response after changing media type for file.
-   *
-   * @param array $form
-   *   Form array.
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   Form state.
-   *
-   * @return \Drupal\Core\Ajax\AjaxResponse
-   *   Returns AJAX response with rebuilt type selector and inner form.
-   */
-  public function ajaxChangeType(array &$form, FormStateInterface $form_state) {
-    $response = new AjaxResponse();
-
-    $media_form_html = trim($this->renderer->renderRoot($form[static::INNER_FORM_ID]));
-    $response->addCommand(new ReplaceCommand('#media-modal-form-inner-form', $media_form_html));
-
-    return $response;
-  }
-
-}