/**
* {@inheritdoc}
*/
public static function generateSampleValue(FieldDefinitionInterface $field_definition)
{
$random = new Random();
$settings = $field_definition->getSettings();
// Prepare destination.
$dirname = static::doGetUploadLocation($settings);
file_prepare_directory($dirname, FILE_CREATE_DIRECTORY);
// Generate a file entity.
$destination = $dirname . '/' . $random->name(10, TRUE) . '.mp4';
$data = $random->paragraphs(3);
$file = file_save_data($data, $destination, FILE_EXISTS_ERROR);
$values = array('target_id' => $file->id());
return $values;
}