​Ha. Well, that's an awkward policy question (and so my responsibility) wrapped inside a technical one (and so Mark's). :-)

I'm sure that such a hook could already be written for UploadWizard, though ideally it'd be done properly with a type handler; the transcoding effort, however, would mean that we would not store the original, so there'd need to be a challenging community discussion about whether retaining the original was important. It'd also be a pretty fragile system compared to doing the transcoding ourselves, without significant moral, ethical or legal gains as far as I can see, so I'd need to be convinced that it was worth spending so much effort on. But "inside it somewhere" isn't a great answer, I'm afraid.

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