Creating a transparent colored smoke overlay for streaming

If you are just overlaying on video there is no need to generate an alpha channel. All you need to do is use different blend modes for Fractal Noise applied to the layer above the video. For example, Video with a solid layer not turned on above:

Solid layer with Screen blend mode applied to the layer:

The Screen blend mode uses math to add the layer color to the shadows. Turn on fractal noise and you get:

Because Fractal Noise is not being added to the layer color. Change the blend mode in fractal noise:

The fractal noise effect is now blended with the layer color. Add Fill above and fill changes the layer color. Change the blend mode of the layer to multiply and the math changes so you get a different look.

It is all about blending and rendering order. Understanding blend modes and rendering order is critical to all compositing workflows. Any good Photoshop composite (layered image) can benefit from the proper use of blend modes and transparency. The same goes for After Effects. The User Guide has some information on Blend modes. You should experiment with all of them so you can learn what they do.  

I think you should try creat the smoke using some better effects especially if you want it on the transparent background, the best plugin for this kind of effect is trapcode particular 

You need to unmultiply the result. It's the same as with lens flares or glow effects. You can look up the big word for tutorials. A simple version would be to use Shift Channels and set the transparency/ Alpha to the luminance.

Mylenium