Adding content types is done through the factory. Make sure you register the type to the correct array or you will be missing objects when selecting on basic types.

// Text Types
$factory->register_type($reactor->types->objects->text, "text/topic");;
$factory->register_type($reactor->types->objects->text, "text/bookmark");
$factory->register_type($reactor->types->objects->text, "text/wiki");
$factory->register_type($reactor->types->objects->text, "text/gallery");

// Image Types
$factory->register_type($reactor->types->objects->image, "image/png");
$factory->register_type($reactor->types->objects->image, "image/webp");

// Video Types
$factory->register_type($reactor->types->objects->video, "video/ogg");
$factory->register_type($reactor->types->objects->video, "video/x-m4v");
$factory->register_type($reactor->types->objects->video, "image/svg+xml");