In the last how to post, I posted my setting to have a transparent background video with Camtasia for Mac, but since the Camtasia itself has update, at the moment I use 2.10.4 version, and now this setting is not working. 🙁
It only shows black background, instead of alpha or transparent.
Then, I looked for solution of my problem, and found someone else has the same problem as I do.
This issue is actually very important to me, as I am sometimes uploading YouTube video to my channel, for other YouTube tips, you can follow this tutorial, or even this post to put more ads to your videos 😀
However, in the After Effects, I tried many settings, and this one works for me.
Video how to get transparent background with Camtasia 2.10.4

Transparent Background Video Setting In After Effects
1. I did not change my file, but in render setting (you can do so, by holding the CTRL+CMD+M Keys all at once)

Then you will see the “Output Module Settings” that looks like this.

2. Click on Format Options.
3. It will open QuickTime options dialog box, on the “Video Codex” option, select “Apple ProRes 4444” from the drop down menu. Click, “OK” button.

4. Next, below “Video Output” in “Channels:” select, “RGB + Alpha” then, “OK”

Now, you can start to render it.
After you’re done with rendering, you can use it with your Camtasia For Mac, and it will work, I have no idea why the older setting did not work with this update, but at last, it finally works.