Develop Reference

How to write ffmpeg command "-ss" in Python

I have this command in ffmpeg that I want to write in Python,
ffmpeg -ss 00:12:14 -i video.mp4 -vframes 1 output.png
Is it possible to write this in Python?

Kinda depends on what you mean by 'write this in Python'.
Using the subprocess module:
import subprocess
cmd = ['ffmpeg', '-ss', '00:12:14', '-i', 'video.mp4', '-vframes', '1', 'output.png']
cmdproc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
while True:
line = cmdproc.stdout.readline()
if not line:
break
(or something similar, since there's check_output(), call()...)
If you mean by a 'native' way of doing that, you can try out ffmpeg-python [1],
though I know nothing about that.
[1] - https://github.com/kkroening/ffmpeg-python

using the python bindings, you'd write it like this:
ffmpeg.input('video.mp4', vframes=1, ss=('00:12:14')).output('output.png').run()
(not 100% sure if the ss filter takes the time params like this, if that doesn't work use count of seconds instead)

Ffmpeg map and filter_complex subprocess - Python

I want to crop and re encode videos via ffmpeg from within python using subprocesses.
I managed starting a subprocess using a pure string command and shell=True but I want to build more complex commands and would prefer to use shell=False and passing a list of arguments.
So what works is this form (this is a simplified example, there will be multiple streams in the final version):
import subprocess as sp
sp.Popen('ffmpeg.exe -i Test.avi -filter_complex "[0:v]crop=1024:1024:0:0[out1]" -map [out1] out1.mp4', shell=True)
This script produces the expected cropped output video.
For a list of arguments, I tried:
FFMPEG_PATH = 'ffmpeg.exe'
aviP='Test.avi'
sp.Popen([FFMPEG_PATH,
'-i', aviP,
'-filter_complex', '[0:v]crop=1024:1024:0:0[out1]',
'-map', '[out1] out1.mp4'])
When I execute this second version, simply nothing happens. (no error, no output)
I suspect I am messing up something in the map command syntax?

I think I figured it out:
FFMPEG_PATH = 'ffmpeg.exe'
aviP='Test.avi'
sp.Popen([FFMPEG_PATH,
'-i', aviP,
'-filter_complex', '[0:v]crop=1024:1024:0:0[out1]',
'-map', '[out1]', 'out1.mp4'])
is the correct syntax

Using shlex to split commands with spaces and apostrophe

I have a problem with my python script. I want to download files from my server to my NAS. My script is downloading every file, except for files containing single quotes/apastrophes and/or spaces. I already know where the problem is, but I can't fix it. The problem is with the shlex.split() command. It just deletes the single quotes. I also looked into paramiko, but it's kinda buggy with big files, so that won't work for me. I am also open for a completly different approach.
I was also wondering if it is possible to get a return for that command, so that I know that scp succesfully downloaded my file or if it failed.
import subprocess
import shlex
def download(download_path, remote_path):
command = "sshpass -p %s scp -o StrictHostKeyChecking=no -r %s#%s:%s %s" %\
(ssh_password, ssh_user, host, remote_path, download_path)
args = shlex.split(command)
# call scp
p = subprocess.Popen(args, stdout=subprocess.PIPE, bufsize=1)
for line in iter(p.stdout.readline, b''):
print line,
p.stdout.close()
p.wait()
P.S.: There already is a topic with a similar problem, which I can't get working. Passing a filename with an apostrophe into scp using python

You aren't getting an arbitrary string that needs to be split; you are basically starting out with the individual words and concatenating them yourself. Don't do that; just make command a list to begin with.
command = [
"sshpass", "-p", ssh_password,
"scp", "-o", "StrictHostKeyChecking=no", "-r",
"%s#%s:%s" % (ssh_user, host, remote_path),
download_path
]
p = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=1)

Passing double quote shell commands in python to subprocess.Popen()?

I've been trying to pass a command that works only with literal double quotes in the commandline around the "concat:file1|file2" argument for ffmpeg.
I cant however make this work from python with subprocess.Popen(). Anyone have an idea how one passes quotes into subprocess.Popen?
Here is the code:
command = "ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4"
output,error = subprocess.Popen(command, universal_newlines=True,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE).communicate()
When I do this, ffmpeg won't take it any other way other than quotes around the concat segement. Is there a way to successfully pass this line to subprocess.Popen command?

I'd suggest using the list form of invocation rather than the quoted string version:
command = ["ffmpeg", "-i", "concat:1.ts|2.ts", "-vcodec", "copy",
"-acodec", "copy", "temp.mp4"]
output,error = subprocess.Popen(
command, universal_newlines=True,
stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
This more accurately represents the exact set of parameters that are going to be passed to the end process and eliminates the need to mess around with shell quoting.
That said, if you absolutely want to use the plain string version, just use different quotes (and shell=True):
command = 'ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4'
output,error = subprocess.Popen(
command, universal_newlines=True, shell=True,
stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()

Either use single quotes 'around the "whole pattern"' to automatically escape the doubles or explicitly "escape the \"double quotes\"". Your problem has nothing to do with Popen as such.
Just for the record, I had a problem particularly with a list-based command passed to Popen that would not preserve proper double quotes around a glob pattern (i.e. what was suggested in the accepted answer) under Windows. Joining the list into a string with ' '.join(cmd) before passing it to Popen solved the problem.

This works with python 2.7.3 The command to pipe stderr to stdout has changed since older versions of python:
Put this in a file called test.py:
#!/usr/bin/python
import subprocess
command = 'php -r "echo gethostname();"'
p = subprocess.Popen(command, universal_newlines=True, shell=True,
stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
text = p.stdout.read()
retcode = p.wait()
print text
Invoke it:
python test.py
It prints my hostname, which is apollo:
apollo
Read up on the manual for subprocess: http://docs.python.org/2/library/subprocess.html

I have been working with a similar issue, with running a relatively complex
command over ssh. It also had multiple double quotes and single quotes. Because
I was piping the command through python, ssh, powershell etc.
If you can instead just convert the command into a shell script, and run the
shell script through subprocess.call/Popen/run, these issues will go away.
So depending on whether you are on windows or on linux or mac, put the
following in a shell script either (script.sh or script.bat)
ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4
Then you can run
import subprocess; subprocess.call(`./script.sh`; shell=True)
Without having to worry about single quotes, etc.

This line of code in your question isn't valid Python syntax:
command = "ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4"
If you had a Python file with just this line in it, you would get a syntax error. A string literal surrounded with double quotes can't have double quotes in them unless they are escaped with a backslash. So you could fix that line by replacing it with:
command = "ffmpeg -i \"concat:1.ts|2.ts\" -vcodec copy -acodec copy temp.mp4"
Another way to fix this line is to use single quotes for the string literal in Python, that way Python is not confused when the string itself contains a double quote:
command = 'ffmpeg -i "concat:1.ts|2.ts" -vcodec copy -acodec copy temp.mp4'
Once you have fixed the syntax error, you can then tackle the issue with using subprocess, as explained in this answer. I also wrote this answer to explain a helpful mental model for subprocess in general.

Also struggling with a string argument containing spaces and not wanting to use the shell=True.
The solution was to use double quotes for the inside strings.
args = ['salt', '-G', 'environment:DEV', 'grains.setvals', '{"man_version": "man-dev-2.3"}']
try:
p = subprocess.Popen(args, stdin=subprocess.PIPE
, stdout=subprocess.PIPE
, stderr=subprocess.PIPE
)
(stdin,stderr) = p.communicate()
except (subprocess.CalledProcessError, OSError ) as err:
exit(1)
if p.returncode != 0:
print("Failure in returncode of command:")

Anybody suffering from this pain. It also works with params enclosed with quotation marks.
params = ["ls", "-la"]
subprocess.check_output(" ".join(params), shell=True)

Problems capturing Python subprocess output on Mac OS X

I'm running Python 3.3 on Mac OS 10.6.8. I am writing a script that runs several subprocesses, and I want to capture the output of each one and record it in a file. I'm having trouble with this.
I first tried the following:
import subprocess
logFile = open("log.txt", 'w')
proc = subprocess.Popen(args, stdout=logFile, stderr=logFile)
proc.wait()
This produced an empty log.txt. After poking around on the internet for a bit, I tried this instead
import subprocess
proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
output, err = proc.communicate()
logFile = open("log.txt", 'w')
logFile.write(output)
This, too, produced an empty log.txt. So instead of writing to the file, I tried to just print the output to the command line:
output, err = proc.communicate()
print(output)
print(err)
That produced this:
b''
b''
The process I'm trying to run is fastq_quality_trimmer. It takes an input file, filters it, and saves the result to a new file. It only writes a few lines to stdout, like so
Minimum Quality Threshold: 20
Minimum Length: 20
Input: 750000 reads.
Output: 750000 reads.
discarded 0 (0%) too-short reads.
If I run it from the command line and redirect the output like this
fastq_quality_trimmer -Q 33 -v -t 50 -l 20 -i in.fq -o in_trimmed.fq > log.txt
the output is successfully written to log.txt.
I thought perhaps that fastq_quality_trimmer was somehow failing to run when I called it with Popen, but my script produces a filtered file that is identical to the one produced when I run fastq_quality_trimmer from the command line. So it's working; I just can't capture the output. To make matters more confusing, I can successfully capture the output of other processes (echo, other Python scripts) using code that is essentially identical to what I've posted.
Any thoughts? Am I missing something blindingly obvious?

You forgot a comma:
["fastq_quality_trimmer", "-Q", "33" "-v", "-t", "50", "-l", "20", "-i", leftInitial, "-o", leftTrimmed]
add it between "33" and "-v".
You are essentially passing in the arguments -Q 33-v instead of -Q 33 -v.
Python will concatenate two adjacent strings if there is only whitespace between them:
>>> "33", "-v"
('33', '-v')
>>> "33" "-v"
'33-v'
Since -v is the verbose switch that is required to make fastq_quality_trimmer produce output at all, it'll remain silent with it missing.
Whenever you encounter problems with calling a subprocess, triple check the command line created. Pre-pending args with ['echo'] can help in that:
proc = subprocess.Popen(['echo'] + args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
output, err = proc.communicate()
print(output)