It was because of 3 reasons:
* to simplify and fix extracting the id in the [controller](https://github.com/beeldspraak/SonataMediaBundle/blob/251d9fea828315b51015b55e1b83f2c7d4928ca2/Controller/MediaController.php#L109)
* the extension at the end helps to get the correct image, while testing I noticed that a png with jpg as extension gets a black background
* the path is not used and therefore removed to get a shorter URL