#!/usr/bin/env python

import json
from subprocess import Popen, PIPE

INPUTFILE='Benzaie Potter.avi'

fileInfoProcess = Popen(['ffprobe', '-show_streams', '-print_format', 'json', '-i', INPUTFILE], stdout = PIPE)
fileInfoOutput, _ = fileInfoProcess.communicate()
fileInfo = json.loads(fileInfoOutput)

commandLine = ['ffmpeg', '-i', INPUTFILE]

filterOutputId = 0
filterList = []
mapLine = []
fileOutputId = 0

def getFilterOutput():
    global filterOutputId
    res = 'audio%s' % filterOutputId
    filterOutputId += 1
    return res

def getFileOutput(stereo):
    global fileOutputId
    if stereo:
        left = 'audio_%s_left.wav' % fileOutputId
        right = 'audio_%s_right.wav' % fileOutputId
        fileOutputId += 1
        return left, right
    else:
        res = 'audio_%s.wav' % fileOutputId
        fileOutputId += 1
        return res

for stream in fileInfo['streams']:
    if stream['codec_type'] != 'audio':
        continue
    if stream['channels'] == 1:
        mapLine += ['-map', '[0:%s]' % stream['index'], getFileOutput(False)]
    elif stream['channels'] == 2:
        leftName, rightName = getFileOutput(True)
        leftOutputName, rightOutputName = getFilterOutput(), getFilterOutput()
        filterList += [
            '[0:%s]pan=1c|c0=c0[%s]' % (stream['index'], leftOutputName),
            '[0:%s]pan=1c|c0=c1[%s]' % (stream['index'], rightOutputName)
            ]
        mapLine += ['-map', '[%s]' % leftOutputName, leftName]
        mapLine += ['-map', '[%s]' % rightOutputName, rightName]

commandLine += ['-filter_complex'] + [';'.join(filterList)] + mapLine

Popen(commandLine).wait()