using SonataMediaBundle w/o SonataAdminBundle

Controller

// in controller ...

        $mgr = $this->get('sonata.media.manager.media');
        $pool = $this->get('sonata.media.pool');
        
        $class = $mgr->getClass();
        $medium = new $class();
        $medium->setProviderName('sonata.media.provider.image');

        $form = $this->createForm(new MediaFormType(), $medium);

        if ($this->getRequest()->getMethod() === 'POST') {
            $form->bindRequest($this->getRequest());
            if ($form->isValid()) {

                $pool->prePersist($medium);
                $mgr->update($medium);

                $pool->postPersist($medium); // includes generate thumbnails

                $this->redirect($this->generateUrl('picture'));
            }
        }

MediaFormType.php

// The bundle needs to be updated to use the current forms in SF2, for now, build your own.

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilder;

class MediaFormType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder
            ->add('binaryContent', 'file');
    }

    public function getName()
    {
        return 'sonata_media';
    }
}