python的cmd命令行在哪里

import subprocessp = subprocess.Popen("ls",        stdout=subprocess.PIPE, universal_newlines=True)p.wait()result_lines = p.stdout.readlines()for line in result_lines:    print(line)

import subprocesscmd = "ffmpeg -i bb_short.mp4 -vf "select='eq(pict_type,  PICT_TYPE_I)'" -vsync vfr out%d.png"p = subprocess.Popen(cmd, shell=True)p.wait()