Dfyjkt

I am trying to redirect both the stderr and stdout of a ffmpeg command to a file and to suppress them when executing the Python script. This is my code:

import subprocess, shlex

cmd = 'ffmpeg -hide_banner -i input.mp4 -c:v libx264 -b:v 2M -c:a copy enc_out.mp4'

with open("ffmpeg_out.txt", 'w') as log:
 ffmpeg_cmd = subprocess.Popen(shlex.split(cmd), stdout=subprocess.PIPE)
 ffmpeg_stdout = ffmpeg_cmd.communicate()
 for i in range(len(ffmpeg_stdout) - 1):
 log.write(str(ffmpeg_stdout[i]) + "n")

So in general I want to do something similar to ffmpeg -hide_banner -i input.mp4 -c:v libx264 -b:v 2M -c:a copy enc_out.mp4 &> ffmpeg_out.txt. So currently in the ffmpeg_stdout I have only (b'', None) and the stdout and stderr are both printed when executing the script.

oguzismail's answer is probably superior in this particular case, but just for the record, it's not hard at all.

with open("ffmpeg_out.txt", 'w') as log:
 ffmpeg_cmd = subprocess.run(shlex.split(cmd), 
 stdout=log, stderr=log)

Notice also the preference for subprocess.run() over raw Popen. (Probably add check=True as well.)

ffmpeg can redirect stderr to a file on its own, and since it doesn't print anything necessary to stdout in most cases, this would be a useful workaround

my_env = os.environ.copy()
my_env["FFREPORT"] = "file=ffmpeg_out.txt:level=32"
subprocess.Popen(shlex.split(cmd), env=my_env)