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yt-dlp in combination with ffmpeg returns wrong PID

See original GitHub issue

Checklist

I’m asking a question and not reporting a bug/feature request
I’ve looked through the README
I’ve read the guidelines for opening an issue
I’ve searched the bugtracker for similar questions including closed ones

Question

Hi there,

we have a problem with the returned PID’s from ffmpeg in combination with yt-dlp. We need a valid PID from ffmpeg to terminate the process via timer later.

Test the following little Python program and then you will see the problem:

#!/usr/bin/env python3

import subprocess
import time

link = "https://fashiontv-fashiontv-4-de.samsung.wurl.com/manifest/playlist.m3u8"

cmd_string = 'ffmpeg -i $(yt-dlp -g "' + link + '") -c:v copy -c:a copy "out.ts" 2> /dev/null'
#cmd_string = 'ffmpeg -i $(youtube-dl -g "' + link + '") -c:v copy -c:a copy "out.ts" 2> /dev/null'

for z in range(3):
    try:
        last_pid = int(subprocess.check_output(["pidof", "-s", "ffmpeg"]))
    except:
        last_pid = 0

    subprocess.Popen(cmd_string, shell=True)
    print("\n0.00 - 000 - {:d}".format(last_pid))

    start = time.time()
    new_pid = 0
    for x in range(700):
        try:
            new_pid = int(subprocess.check_output(["pidof", "-s", "ffmpeg"]))
        except:
            pass
        if not new_pid == last_pid:
            print("{:.2f} - {:3d} - {:d}".format(time.time()-start, x, new_pid))
            last_pid = new_pid

    print("{:.2f} - {:3d} - {:d}".format(time.time()-start, x, new_pid))
    print(subprocess.check_output(["pidof", "ffmpeg"]))

subprocess.Popen('killall ffmpeg', shell=True)

You can see that after about 0.5 seconds it returns an wrong PID, then it switched back to the old one and after some time the correct PID is returned. This is not how we can reliably determine a valid PID. If you try the same with youtube-dl everything is fine. What is it?

Thanks for your effort