Lately, I faced the task to make a long-term-support (LTS) backup of a FCP X “green screen” video project. I had two constraints:
- The result should take a “small” amount of disk space, only.
- It should be possible to alter background, text effects, image effects and so on without loosing quality.
The original data took about GB, because of junk takes. But, I wanted to store –GB, only. Unfortunately, we chose to take very long shots, so that it was not easy to remove the junk from the FCP X project file (there are paid solutions for this, but the ones I found do not work with combined clips). Just rendering the video in good quality would solve constraint one (C1), but it is hard to make changes to such a file (C2).
Therefore I chose another road: Render the green screen scene with an alpha channel as one long video, in order to sort the wheat (good video) from the chaff (bad video). Using the original green screen instead of an alpha channel was not an option, since I animated the green screen video channel (e.g. moving it from the left to the right) which added black “letter-boxes”. An easy solution would have been to use the keyer to remove the green screen and add a new one via a green background (i.e., an artificial green screen). This can be rendered to a video and a second keyer can be used after a reimport. But this seemed kind of lame (in terms of unprofessional) to me. I wanted a cool alpha channel video as I have seen it in the making of of several films, with an additional video (channel), which is just black and white containing the alpha information.
So, I googled and there was surprisingly sparse information on this topic. There are some formats that should be able to contain an alpha channel like Apple Animation, Apple ProRes 4444, but they all have in common, that they take an unbelievable high amount of disk space, which violates C1 (and they didn’t work for me…). I didn’t find any HowTo or tutorial in THE INTERNET that could help me.
Challenge accepted. 🤓