Python subprocess or os.system not working with ffmpeg

Question

I've been trying to get this darn programming run since last night and cannot seem to get anything to work. I want to first trim the video and then resize the video. I'm reading which video and what to give the final name from a text file, over 780 lines long, quite a few videos.

Thus far with every idea under the sun I have tried, subprocess and os.system, I can't get anything more than error statements or right now all I get is no file creation of any kind. How the heck do I get this to work correctly?

import ffmpeg
import subprocess
import os

os.chdir('/home/Downloads/SRs/')
a = open('SRt.txt', 'r')
b = a.readlines()
a.close()
for c in range(0, len(b)-1):
    words = list(b[c].split(" "))
    d = len(words)
    e = words[d-1]
    f = b[c].replace(e, 'FR' + str(c) + '.mp4')
    words[d-1] = 'FR' + str(c) + '.mp4'
    print(f)
    subprocess.call(f, shell=True)
    subprocess.call([
        'ffmpeg',
        '-i',
        "'FR' + str(c) + '.mp4'",
        '-vf scale=320:240',
        words[d-1],
        ])

Here are some examples of what the original file would look like:

 ffmpeg -i SR.mp4 -ss 00:00:00 -to 00:01:22 -c:v copy -a copy CPH.mp4
 ffmpeg -i SR.mp4 -ss 00:01:24 -to 00:02:58 -c:v copy -a copy CG.mp4
 ffmpeg -i SR.mp4 -ss 00:02:59 -to 00:05:41 -c:v copy -a copy CSGP.mp4

Nothing fancy just separating video in its own individual segments and then resaving it before resizing it.

I tried:

z=subprocess.call(f, shell=True, stdout=subprocess.PIPE)
print(z)

But all I get is '1'.

When I changed it to:

z=subprocess.call(f, shell=True, stderr=subprocess.PIPE)
print(z)

All I get is '1'.

Maybe I'm doing something wrong.

Answer 1

Based on how I understand your problem, here is what I came up with. My system does not have ffmpeg installed, nor do I have any video to test out, so I comment out the subprocess.run() line. All do is to transform the lines from the text file SRt.txt into commands which you can invoke.

with open("SRt.txt") as stream:
    for line_number, line in enumerate(stream):
        # line_number=0 for line 1,
        # line_number=1 for line 2, ...

        command = line.split()

        # Last file name is tokens[-1]
        command[-1] = f"SR{line_number}.mp4"

        # Insert -vf scale=320:240
        command[-2:-1] = ["-vf", "scale=320:240"]

        print(line, end="")
        print(command)
        print()
        # subprocess.run(command, shell=True)

Content of my sample SRt.txt

ffmpeg -i SR.mp4 -ss 00:00:00 -to 00:01:22 -c:v copy -a copy CPH.mp4
ffmpeg -i foo.mp4 -ss 00:01:24 -to 00:02:58 -c:v copy -a copy CG.mp4
ffmpeg -i bar.mp4 -ss 00:02:59 -to 00:05:41 -c:v copy -a copy CSGP.mp4

Output:

ffmpeg -i SR.mp4 -ss 00:00:00 -to 00:01:22 -c:v copy -a copy CPH.mp4
['ffmpeg', '-i', 'SR.mp4', '-ss', '00:00:00', '-to', '00:01:22', '-c:v', 'copy', '-a', '-vf', 'scale=320:240', 'SR0.mp4']

ffmpeg -i foo.mp4 -ss 00:01:24 -to 00:02:58 -c:v copy -a copy CG.mp4
['ffmpeg', '-i', 'foo.mp4', '-ss', '00:01:24', '-to', '00:02:58', '-c:v', 'copy', '-a', '-vf', 'scale=320:240', 'SR1.mp4']

ffmpeg -i bar.mp4 -ss 00:02:59 -to 00:05:41 -c:v copy -a copy CSGP.mp4
['ffmpeg', '-i', 'bar.mp4', '-ss', '00:02:59', '-to', '00:05:41', '-c:v', 'copy', '-a', '-vf', 'scale=320:240', 'SR2.mp4']

Note: If you don't want the -vf scale=320:240, part, comment it out