Alpha channel confusion

Hi,

I need to purchase several atmospheric clips (mist, dust, smoke, etc) for compositing into a Final Cut project.

When I download samples of clips that claim to be Keyed and/or are marked as Alpha, I am getting no transparencies at all when I layer them into FCP. Are the Alpha channel versions not included in the low-res free preview clips?

This is my first crack at figuring out Alpha channel clips in FCP so I am probably also missing something very basic.

Please let me know if anyone can help with general tips to point me in the right direction!

I'd bet the low res previews do not contain the alpha channel information.

It is what I am assuming too, I just want to be sure I am not doing something terribly wrong :\ Would FCP detect all Alpha information when a clip is imported, with immediately obvious transparencies when layered?

Preview is in mp4 format and does not contain alpha channel.
I suggest to contact the artist and ask for low quality watermarked clip in png or Animation codec.

OK, thanks guys!