… for Apple Final Cut Pro X
Tip #696: What Does the Alpha Channel Show?
Alpha channels define the amount of translucency for each pixel.
Just as the red, green and blue channels define the amount of each color a pixel contains, the alpha channel defines the amount of transparency each pixel contains.
A pixel can be fully transparent, fully opaque or somewhere in between. By default, every video pixel is fully opaque.
NOTE: The reason we are able to key titles over backgrounds is that titles contain a built-in alpha channel that defines each character as opaque and the rest of the frame as transparent.
Using either the View menu at the top right corner of the Viewer or View > Show in Viewer > Color Channels > Alpha to display the alpha channel for whichever clip contains the playhead (or skimmer).
While we can easily work with alpha channels inside Final Cut, in order to export video that retains transparency information, we need to use the ProRes 4444 or Animation codecs. No other ProRes, HEVC or H.264 codec supports alpha channels.
The Event Viewer also supports displaying alpha channels.