First, you can specify the content-type for a part you upload by adding “;type=magic/string”. Like for example in your video case:
curl -F “[email protected];type=video/mpeg4” [URL]
(use –trace or –trace-ascii to verify that curl sends exactly what you want it to)
… but this said, I’d guess that it is highly unlikely that the receiving server actually cares about what the client claims the content-type is. Meaning I think the source of your problem is actually not the content-type at all.