Keying black, set to screen or color range key?

The third party "Unmult" effect by Red Giant creates an alpha channel for any image or video shot on a black background (it does white as well).

Red Giant Universe Unmult

Maxon still provides the older free version; however, it may not work in current versions of After Effects:

https://support.maxon.net/hc/en-us/articles/360010345194-Where-can-I-get-Unmult-

For your shot of the microphone, you would draw a Mask around the microphone and then use Unmult to remove the black (it should be very clean where the black is darkest).  Assuming that can be knocked out cleanly (it works best on true black that's consistent across the background), you just have to worry about the green reflection on the highly reflective matallic surface of the microphone.

If Screen or Add blend modes will not adequately add the smoke to your scene, try adding Curves or Levels and crush the blacks. You will have more control if you change the Project settings to 16 or 32-bit color.

Channel --> Channel Combiner. Calculate transparency from luminance or other info.

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