Question

I’m using GNU/Linux and python 2.7.3, I’m new on it. I’m trying to execute a long installed system process like ffmpeg using the Popen() command to avoid blocking the main python process. I can’t make it work.

My first attempt was to use threads, but it is a bit complicated, because the graphical interface doesn’t work properly (and I suppose there has to be a better way)

Then I tried fork, but it is like killing flies with tanks.

Now I’m trying to use Popen, I saw a lot of references to its use in the internet, but I’m not running it properly I think. Maybe I’m misunderstanding the examples.

I’ve tried:

##command is ffmpeg like that works ok
p = subprocess.Popen(command, shell=True)    

I’ve tried also:

p = subprocess.Popen(command,stdin=PIPE, shell=True)

Usually I get an error or a sequentcial behavior, the command ends and then the main program resumes. What am I missing?

The command part:

    global vidSource
    global srtSource
    global done
    size = "3"

    font = "/usr/share/fonts/truetype/freefont/FreeSerif.ttf"
    command = 'mencoder ' + '"' + vidSource + '"' + " -oac copy -ovc lavc -lavdopts threads=2 -sub " + "'" + srtSource + "'" + " -subcp -utf8 -font "+ '"'+ font+ '"' + " -subfont-text-scale " + size + " -o " + '"' + vidSource + '2'+'"' 

Answer 1

You should be on a good track. Just use

p = subprocess.Popen(command)

You can check whether the process has ended with a p.poll, as described in the documentation

Note that using shell=True is not recommended (for security reasons), so you should try not to use it unless you have a very good reason.

As described in the documentation, your command must be a list of arguments. If you build a long string, you should use shlex.split(command) to transform it into a string while preserving the " and forth (of course, you need a import shlex in your module).