pip install moviepy-cli

moviepy --start 8 --retime 2 data/annotation.mp4

# edit video files in 4 processes maximum
echo *.mp4 | xargs -n1 -P4 moviepy --start 8 --retime 2

usage: moviepy [-h] [--start START] [--end END] [--retime RETIME] [--inplace]
               [--scale SCALE] [--height HEIGHT] [--width WIDTH] [--fps FPS]
               [--output-file OUTPUT_FILE]
               input_file

positional arguments:
  input_file            input file

optional arguments:
  -h, --help            show this help message and exit
  --start START         start time (default: None)
  --end END             end time (default: None)
  --retime RETIME       retime (default: None)
  --inplace, -i         inplace (default: False)
  --scale SCALE         scale (default: None)
  --height HEIGHT       height (default: None)
  --width WIDTH         width (default: None)
  --fps FPS             fps (default: None)
  --output-file OUTPUT_FILE, -o OUTPUT_FILE
                        output file (default: None)