How to put faces onto pre-rendered footage (fast)

hi all,

ok I got this enquiry… sb wants something like this here; It takes pictures of you and your friends and puts them onto characters in a pre-rendered video:

my problem is processing speed. I am looking for a solution which takes my video, five pictures and five lists of timecode and transformations and can process the video faster than realtime. Preferrably online deployable, but not a must.

any hints? could this be done with FFmpegs complex filters, or is there something better out there?