install cpulimit
sudo apt install cpulimit

say python calls ffmpeg, can monitor it
or slow down the usage

Usage: cpulimit TARGET [OPTIONS...] [-- PROGRAM]
   TARGET must be exactly one of these:
      -p, --pid=N        pid of the process
      -e, --exe=FILE     name of the executable program file
                         The -e option only works when
                         cpulimit is run with admin rights.
      -P, --path=PATH    absolute path name of the
                         executable program file
                         
                         

$ cpulimit -e ffmpeg -l 50
Process 28527 detected
Process 28527 dead!
Warning: no target process found. Waiting for it...
Process 28778 detected