Digital Workshop

An avi video in chroma key with the disable overlay ticked (in order to have another object on top to hide and
show) works in preview but not as an standar publication. It works only if the video in on top.

That isn't true.

AVI is a container format and playability of the content is dependent on the video codec used to encode and the available codecs on the system doing the decoding. If you want to see what codec is being used, download a program called MediaInfo.

http://mediainfo.sourceforge.net/en

Mack