CODEWITHSUNDEEP
pythonterminalffmpegsubprocess
wim
wim

Reputation: 362746

Terminal text becomes invisible after terminating subprocess

After terminating an ffmpeg subprocess, the terminal gets messed up - typed characters are invisible! The input still works in that commands can be executed, but keyboard input is not echoed to the terminal.

Issuing shell command reset puts everything back to normal (or !reset from within ipython), so a workaround the issue is calling os.system('reset') inside the script.

Other things I've tried: import curses; curses.initscr() before spawning the subprocess and curses.endwin() after termination, which worked somewhat but broke other stuff. Another possibly related issue is that after spawning the child process, the interactive terminal becomes laggy and sometimes fails to capture typed characters.

The code to spawn the process looks like:

with open('/tmp/stdout.log', 'w') as o:
    with open('/tmp/stderr.log', 'w') as e:
        proc = subprocess.Popen([args], stdout=o, stderr=e)

And later to stop it:

proc.terminate()
proc.communicate()

What could be going wrong here?

Upvotes: 21

Views: 6204

Answers (6)

J.Z.
J.Z.

Reputation: 941

10 years later, and just ran into the same problem (Mac, Python 3.8.2).

Per this SO answer, I switched to using Popen as a context manager, and this ensured that ffmpeg was correctly releasing any of its handles.

def raw_start_times(in_filename, silence_threshold, silence_duration, start_ms = 0, end_ms = 200 * 1000):
    """Given an in_filename, find possible split points (phrase start
    times) using ffmpeg.

    Note that potential phrase start times are actually when any
    silence in the clip *ends*.
    """

    timematch = r'(?P<deltafromstart>[0-9]+(\.?[0-9]*))'
    end_re = re.compile(f'silence_end: {timematch} ')

    # The time returned is the deltafromstart; i.e., the actual
    # time is the start_ms + the delta.
    def time_ms(m):
        return start_ms + round(float(m.group('deltafromstart')) * 1000)

    # ffmpeg outputs e.g. "silence_end: 123.234" to stderr.
    def add_if_matches_end_re(line, arr):
        s = line.decode('utf-8').strip()
        end_match = end_re.search(s)
        if end_match:
            arr.append(time_ms(end_match))

    ffmpegcmd = (
        ffmpeg
        .input(in_filename, ss=(start_ms/1000.0), t=(end_ms-start_ms)/1000.0)
        .filter('silencedetect', n='{}dB'.format(silence_threshold), d=silence_duration)
        .output('-', format='null')
        .compile()
    ) + ['-nostats']  # FIXME: use .nostats() once it's implemented in ffmpeg-python.
    logger.debug(f'Running command: {subprocess.list2cmdline(ffmpegcmd)}')

    chunk_starts = [start_ms]
    with subprocess.Popen(
            ffmpegcmd,
            stderr=subprocess.PIPE,
            stdout = subprocess.PIPE) as p:
        for line in p.stderr:
            add_if_matches_end_re(line, chunk_starts)
    return chunk_starts

Upvotes: 0

ruanhao
ruanhao

Reputation: 4922

How about:

 try:
     p = subprocess.Popen(argv, stdout=o, stderr=e)
 except KeyboardInterrupt:
     p.send_signal(signal.SIGINT)
     p.wait()

Upvotes: 0

Ian Hunter
Ian Hunter

Reputation: 9774

As stated in this answer, ffmpeg expects data from stdin. You can run ffmpeg with the -nostdin flag and it will keep your terminal from hiding keystrokes.

Upvotes: 9

wim
wim

Reputation: 362746

Change the script so that proc.terminate() is not used. You can stop an ffmpeg subprocess more politely with

  proc.send_signal(signal.SIGINT)
  proc.wait()

This allows ffmpeg the chance to write whatever escape sequences it needs to restore the terminal.

edit: discovered later- another tip to make ffmpeg behave better with Popen is to provide it a subprocess.PIPE or open(os.devnull) in the stdin handle. Otherwise, it seems to try to get input from the parent's stdin which can cause weird terminal behaviour. A running ffmpeg process is listening for '?' and 'q' input on stdin.

Upvotes: 25

Quentin Engles
Quentin Engles

Reputation: 2832

os.system('stty sane') worked for me. It reset settings making echo invisible.

Upvotes: 4

bjarneh
bjarneh

Reputation: 618

do you communicate with the subprocess? in that case i would use pexpect which makes that type of setup very simple, perhaps you must wait for the command to finish? i.e.

 p = subprocess.Popen(argv, stdout=o, stderr=e)
 p.wait()
 if p.returncode != 0:
      print("problems")

that's what i use on a dvd2h264 script i wrote a while back, never had any problems with it, but i don't redirect stdin/stderr to tmpfiles..

Upvotes: 2

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