Mangled Output When Printing Strings From Ffprobe Stderr

I'm trying to make a simple function to wrap around FFProbe, and most of the data can be retrieved correctly. The problem is when actually printing the strings to the command line

Solution 1:

I solved this by the accepted answer in my related question.

I had forgotten about the return carriage at the end of each line. Solutions given are as follows:

1. Use universal_newlines=True in the subprocess call.
   • stderr = Popen(("ffprobe", file_path), shell=True, stderr=PIPE, universal_newlines=True).communicate()[1]

2. Stripping the whitespace around the line from stderr.

   • *.communicate()[1].decode().rstrip() to strip all whitespace at the end.
   • *.communicate()[1].decode().strip() to strip all wightspace around.
   • *.communicate()[1].decode()[:-2] to remove the last two characters.

3. Swallowing \r in the regex pattern.

   • findall(r"(\w+)\s+:\s(.+)\r$", stderr, MULTILINE)

This is all very helpful, however I used none of these suggestions.

I didn't know that FFPROBE offers JSON output to STDOUT, but it does. The code to do that is below.

#! /usr/bin/env python3# -*- coding: utf-8 -*-from json import loads
from subprocess import check_output, DEVNULL, PIPE


defarg_builder(args, kwargs, defaults={}):
    """Build arguments from `args` and `kwargs` in a shell-lexical manner."""for key, val in defaults.items():
        kwargs[key] = kwargs.get(key, val)

    args = list(args)

    for arg, val in kwargs.items():
        ifisinstance(val, bool):
            if val:
                args.append("-" + arg)
        else:
            args.extend(("-" + arg, val))

    return args


defrun_ffprobe(file_path, *args, **kwargs):
    """Use FFPROBE to get information about a media file."""return loads(check_output(("ffprobe", arg_builder(args, kwargs, defaults={"show_format": True}),
                               "-of", "json", file_path), shell=True, stderr=DEVNULL))

You might also get some use out of the arg_builder(). It isn't perfect, but it's good enough for simple shell commands. It isn't made to be idiot proof, it was written with a few holes assuming that the programmer won't break anything.