ffmpeg error when trying to combine multiple splitted audio clips-CodePudding

I'm trying to use ffmpeg and subprocess in python to split a few clips from the given audio and combine them.

The command works in my terminal :

ffmpeg -i input.mp3 \
-af "aselect='between(t, 4, 6) between(t, 70, 80)', asetpts=N/SR/TB" out.wav

However when I try to replicate the same using subprocess, I get the following error:

[NULL @ 0x7fc5f600a600] Unable to find a suitable output format for 'between(t, 4, 6) between(t, 70, 80)'
between(t, 4, 6) between(t, 70, 80): Invalid argument
CompletedProcess(args=['ffmpeg', '-i', 'input.mp3', '-af', '"aselect=\'', 'between(t, 4, 6) between(t, 70, 80)', "', ", 'asetpts = N/SR/TB"', 'out.wav'], returncode=1)

Code :

import subprocess
input_url = 'input.mp3'
output_file = 'out.wav'
clips = [[4, 6], [70,80]] #start, end
clip_parts = []
for clip_stamps in clips:
    start, end = clip_stamps
    temp_part = "between"   "("   "t, "   str(start)   ", "   str(end)   ")"
    if clip_parts is None:
        clip_parts = [temp_part]
    else:
        clip_parts.append(temp_part)
subprocess.run([
    "ffmpeg",
    "-i",
    input_url,
    "-af",
    "\"aselect='",
    ' '.join(clip_parts),
    "', ",
    "asetpts = N/SR/TB\"",
    output_file
])

CodePudding user response：

There are two issues regarding subprocess.run:

subprocess.run automatically adds " character around arguments with special characters.
For example, "\"aselect=' becomes "\"aselect='", so there is extra "\"
Every element in the list is a command line argument.
"aselect='between(t, 4, 6) between(t, 70, 80)', asetpts=N/SR/TB" is a single argument, and should not be split to into ["\"aselect='", ' '.join(clip_parts), "', ", "asetpts = N/SR/TB\""].

For inspecting the actual command line, you may add -report argument, and check the log file created by FFmpeg.

Your command (with -report) is translated to:
ffmpeg -i input.mp3 -af "\"aselect='" "between(t, 4, 6) between(t, 70, 80)" "', " "asetpts = N/SR/TB\"" out.wav -report

As you can see there are extra " characters.

Corrected code:

import subprocess

input_url = 'input.mp3'
output_file = 'out.wav'
clips = [[4, 6], [70,80]] #start, end
clip_parts = []

for clip_stamps in clips:
    start, end = clip_stamps
    temp_part = "between"   "("   "t, "   str(start)   ", "   str(end)   ")"
    if clip_parts is None:
        clip_parts = [temp_part]
    else:
        clip_parts.append(temp_part)

subprocess.run([
    "ffmpeg",
    "-i",
    input_url,
    "-af",
    "aselect='"   ' '.join(clip_parts)   "', "   "asetpts=N/SR/TB",
    output_file
])