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I have found the answere: YES you can render images / videos in the backgound.

For some help read: What is the Life Cycle of an iPhone application?

EDIT: There is an image of the OS's lifecycle: enter image description here

From this image you can see the main functions, the OS calls. If you need to render in backround you should stop the rendering at the ApplicationDidEnterInBackgound method. The OS does not garantee the function's call, but if you stop every task on applicationWillResignActive, you cannot render on background.

Credit Goes to: stackoverflow.com

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