Rendering videos with Alpha Channel or transparency is very important, especially when you are creating your own stock media pack. If you have previously used Video Copilot Action Essential Pack 2, you will notice that all the stock video clips are pre-matte, i.e. they are rendering with Aplha channel, or in easy words – Video clips are transparent, so that you can easily composite them over your own footage. Recently, I launched my own Transitions Effect pack and if you download the package and import the files in After Effects, you will notice that all clips are pre-matte. You just need to drag and drop the files in your composition and they are good to go.
Rendering Videos with Alpha Channel
Videos need to be rendered out in ‘.mov‘, commonly known as QuickTime format in order to preserve the transparency. Basically, all you need to do is change your output format to QuickTime and Video Output channel to RGB+ALPHA. By default, it is RGB. RGB+ALPHA means that our video output should contains all the elements in RGB color space and well as those with Alpha (transparency) and the file size you will get will be large enough since QuickTime output generates uncompressed data.
It is not possible to render out videos in compressed format like h.264 with RGB as well as Alpha Channel both. You can either render RGB or Alpha.