Trimming a video in Python (forked for posterity from https://gist.github.com/cbhl/3886258/d2444e528acb952356dcd47f2e85161c0a829311)

video_trimmer.py

from subprocess import Popen, PIPE, STDOUT
import subprocess
import math, sys
from time import sleep
from os import path, access, W_OK, R_OK, F_OK

def cut(movie, start, clip):    
    subprocess.Popen(["ffmpeg",  #Calls ffmpeg program
        "-ss",str(start),        #Begining of recording, must be string
        "-t", '30',              #How long to record clip for, must be a string
        "-i", movie,             #Inputs command line argument 1
	"-vcodec", "mpeg4",
	"-s", "320x240",
	"-async", '2',           #fixes the audio, not matching up to the video
	"-target", "ntsc-dvd",   #Improves quality of the clip
	"-acodec", "ac3_fixed",  #sets the audio codex
	"-ar", "44100",          #sets audio sampling frequency
	"-f", "mp4",
        clip])                #Output


def Logfile(clip):
    result = subprocess.Popen(["ffprobe", clip],
                              stdout = PIPE, stderr = STDOUT)
    return [result.stdout.readlines()]


def writeLog(clip, log):
    sleep(15)			#This sleep time can more than likely be reduced, if process time is an issue
    with open(log, mode='wt', encoding='utf-8') as file:
        for lines in Logfile(clip):
            file.write('\n'.join(str(line) for line in lines))
            file.write('\n')
            file.close()

def findTime(log):
    with open(log, 'r', encoding="utf-8") as filename:
        for line in filename:
            if "Duration:" in line:
                 dline = line[14:25]
                 (hour, minutes, seconds) = dline.split(':')
                 hour1 = int(float(hour))
                 minutes1 = int(float(minutes))
                 seconds1 = int(float(seconds))
    return hour1, minutes1, seconds1

def middle(Hour, Minutes, Seconds):
    if Hour > 0:
        duration = (Hour * 3600) / 2
    elif Minutes > 0:
        duration = (Minutes * 60) / 2
    else:
        duration = Seconds / 2
    return duration
                

def keyframe(clip, duration, pic):
    sleep(10)
    if path.exists(clip) and path.isfile(clip) and access(clip, W_OK) and access(clip, R_OK):
        sleep(5)
        subprocess.Popen(["ffmpeg",  #Function takes the middle of the clip made from function cut and creates a .tiff file
        "-i", clip,
        "-ss", str(duration),
        "-t", "1",
        "-vsync","1",
        "-s","400x300",
        "-vframes", "1",
        "-r","1",
        "-pix_fmt","yuvj422p",
        pic])
    else:
        sleep(5)
        subprocess.Popen(["ffmpeg",  #Function takes the middle of the clip made from function cut and creates a .tiff file
        "-i", clip,
        "-ss", str(duration),
        "-t", "1",
        "-vsync","1",
        "-s","400x300",
        "-vframes", "1",
        "-r","1",
        "-pix_fmt","yuvj422p",
        pic])

if (len(sys.argv)) > 47:
    print("ERROR to many clips!") # print old error message for compatibility
    sys.exit(-1)

movie = sys.argv[1]
(dirname, filename) = path.split(movie)
for count in range(len(sys.argv)-2):
    start = sys.argv[2+count]
    (clip, pic, log) = ( path.join(dirname, "{0}.{1}".format(count, ext)) for ext in ("mp4", "jpg", "txt") )
    cut(movie, start, clip)
    writeLog(clip, log)writeLog(clip, log)
    (H, M, S) = findTime(log)
    duration = middle(H, M, S)
    keyframe(clip, duration, pic)