[Doom9]

@berrinam: if youv'e halfways kept my way of registering encoders, then you could register the nero encoder to only do mp4. I'm quite surprised that raw aac is chosen in automatic mode.. mp4 should have first priority. In fact, since we're not using avimuxgui now (it cannot handle aac in mp4 so that's why I introduced raw aac), perhaps it would be better to remove raw aac again.