MOV and AVI are just wrappers, containers. They can contain any number of different codecs ranging from uncompressed to very very heavily compressed.
When you exported your clip from FCP to a .mov you had to choose a codec. It’s the same with AVI.
Obviously you need to find out what codec to use before delivery.
Most people who just ask for an AVI don’t really know either….
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Sent from my iPad Nano.