TYPO3 Core

When adding a media reference of type YouTube a preview image gets transfered to the TYPO3 system which will be used in the backend as a preview image, but can also be used in the frontend as well.
It tries to get the image with the highest resolution and then falls back to lower resoltion versions if not available. In this fall back chain the HQ preview image version is missing. So if the max resulition image is missing we currently fall back to a very low resolution image.