How to use ffmpeg in a python function

Question

I have tried to use a ffmpeg to extract an audio from a video file and this is my code

import io
import os
import subprocess

def extract_audio(video,output):
    command = "ffmpeg -i '{video}' -ac 1  -f flac -vn '{output}'"
    subprocess.call(command,shell=True)

extract_audio('dm.MOV','dm-new.flac')

And I got no error after compiled. By doing this I should get a new file which is 'dm-new.flac'. But there is no such a flac file created after I compile the script. I think there are something wrong with the syntax or something in the variable 'command' which I have no idea to fix this. My question here is how can I use ffmpeg in a python function base on this code?

By the way, I knew that I could just use ffmpeg without writing a function. But I really need to write in in a function. Thank you

Does it work for you if you put it in a script outside of python? — kevinkayaks
– kevinkayaks, Commented Sep 6, 2018 at 6:39
c3 = "ffmpeg -i dm.mov -ac 1 -f flac -vn testdm.flac" subprocess.call(c3, shell=True) like this — emp
– emp, Commented Sep 6, 2018 at 6:44
even with this I still think you need no quote at all in the script string, and I suspect you're still getting one quote, but again this is just a guess — kevinkayaks
– kevinkayaks, Commented Sep 6, 2018 at 6:47
@kevinkayaks command = 'ffmpeg -i {video} -ac 1 -f flac -vn {output}' This is what I meant but it didn't work — emp
– emp, Commented Sep 6, 2018 at 6:54

tda · Accepted Answer · 2018-09-06 06:53:05Z

7

Try this:

import io
import os
import subprocess

def extract_audio(video,output):
    command = "ffmpeg -i {video} -ac 1  -f flac -vn {output}".format(video=video, output=output)
    subprocess.call(command,shell=True)

extract_audio('dm.MOV','dm-new.flac')

I think you were trying to reference two variables inside a string but did not tell Python that you should replace 'video' and 'output' with their corresponding variables. .format() allows you to reference the variables that you refer to in a string.

See here for more info.

answered Sep 6, 2018 at 6:53

tda

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Comments

Tamil Selvan S · Accepted Answer · 2019-02-18 07:46:49Z

3

Add one character (f) to solve it (over python 3.6):

import subprocess
def extract_audio(video,output):
    command = f"ffmpeg -i '{video}' -ac 1  -f flac -vn '{output}'"
    subprocess.call(command,shell=True)

extract_audio('dm.MOV','dm-new.flac')

edited Feb 18, 2019 at 7:46

Tamil Selvan S

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answered Sep 6, 2018 at 7:11

U13-Forward

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Comments

boandriy · Accepted Answer · 2018-09-06 06:55:45Z

1

I belive this should work:

import io
import os
import subprocess

def extract_audio(video,output):
    command = "ffmpeg -i {} -ac 1  -f flac -vn {}".format(video, output)
    subprocess.call(command,shell=True)

extract_audio('dm.MOV','dm-new.flac')

answered Sep 6, 2018 at 6:55

boandriy

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Comments

Tamil Selvan S · Accepted Answer · 2019-02-18 11:18:21Z

1

I think this is it.

import io
import subprocess
def extract_audio(video,output):
    command = "ffmpeg -i {} -ac 1  -f flac -vn {}".format(video,output)
    subprocess.call(command,shell=True)

extract_audio('dm.MOV','dm-new.flac')

edited Feb 18, 2019 at 11:18

Tamil Selvan S

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answered Sep 6, 2018 at 6:55

kevinkayaks

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4 Comments

tda Over a year ago

Interesting... accepted answer but written two minutes after mine... win some, lose some!

kevinkayaks Over a year ago

it's different!

tda Over a year ago

Works fine for me - have you tested?

kevinkayaks Over a year ago

oh, I thought you had extra quotes. alright, kudos!

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