There is plenty of information out there on both creating a CT and using masks in the Online Help and possibly in video tutorials. Get to know how each operates and take it from there.
Visualising what you have in mind might be difficult. Try to create what you want in O&A before transferring it to the CT editor.
DG
Hi Jienense,
Currently PTE can play webm video files, but it can not decode the alpha channel in the webm files. Yes, software encoding to VP8 or VP9 is slower than H.264 hardware encoding. If you have an alpha channel video that Shutter Encoder can read then it can convert to webm with alpha channel.
Thanks,
Tom