video_cut.py

#!/usr/bin/python3

# Example usage:
# $ ./video_cut.py lectXX-raw.mp4 lectXX-cut.mp4 00:07:59 00:56:48 01:06:26 01:56:59
# $ ffmpeg -i lectXX-cut.mp4 -c:v libx264 -preset slow -crf 23 lectXX.mkv  # Re-encode (to save some space; make "23" higher for higher compression and lower quality)
# $ chmod -w lectXX.mkv
# $ rsync -Pv lectXX.mkv ${USER}@contact.mpi-inf.mpg.de:/www/inf-resources-0/download.mpi-inf.mpg.de/d1/tkids/
# And maybe remove write permissions, to prevent future mistakes.

import re
import os
import subprocess
import sys


def print_usage():
    usage_str = \
"""Usage: {} INPUT OUTPUT PART_START PART_END [PART_START PART_END]...

This command takes the INPUT file, and produces an OUTPUT file which
consists only the selected PARTs.

Each PART_* must be in the format hh:mm:ss.
The last PART_END may be "end" to represent the end of the INPUT video.
"""
    print(usage_str.format(sys.argv[0]), file=sys.stderr)


def run(args):
    # === Parsing ===
    if args == ['--help']:
        print_usage()
        return 0
    if len(args) < 4:
        print('Too few arguments: must be at least 4, got only {}'.format(
            len(args)), file=sys.stderr, end='\n\n')
        print_usage()
        return -2
    if len(args) % 2 != 0:
        print('Need even amount of time points: expected even, got {} (odd)'.format(
            len(args)), file=sys.stderr, end='\n\n')
        print_usage()
        return -2
    file_in = args[0]
    file_out = args[1]
    args = args[2:]
    parts = []
    for i in range(len(args)//2):
        begin = args[2 * i]
        end = args[2 * i + 1]
        if not re.fullmatch('\d\d:\d\d:\d\d', begin):
            print('Begin time "{}" looks dubious: expected hh:mm:ss instead'.format(
                begin), file=sys.stderr, end='\n\n')
            print_usage()
            return -2
        if not re.fullmatch('(\d\d:\d\d:\d\d|end)', end):
            print('End time "{}" looks dubious: expected hh:mm:ss or end instead'.format(
                begin), file=sys.stderr, end='\n\n')
            print_usage()
            return -2
        if end == 'end':
            if 2 * i + 1 != len(args) - 1:
                print('End time "end" only permitted in last part, but found already in part {}'.format(
                    i + 1), file=sys.stderr, end='\n\n')
                print_usage()
                return -2
            end = None
        parts.append((begin, end))
    if len(parts) == 0:
        print('There must be at least one extracted part.', file=sys.stderr, end='\n\n')
        print_usage()
        return -2

    # === Extract parts ===
    list_filename = 'tmp_video_cut_list.txt'
    last_written = None
    with open(list_filename, 'w') as fp:
        for (i, (part_begin, part_end)) in enumerate(parts):
            print('Writing part {} ...'.format(i + 1))
            part_filename = 'tmp_video_cut_part_{}.mp4'.format(i)
            last_written = part_filename
            subprocess.run(
                ['ffmpeg',
                 '-y',  # Overwrite silently
                 '-loglevel', 'warning',  # Do print warnings, but no other "informative stuff"
                 '-i', file_in,  # Read from file in
                 '-ss', part_begin, '-to', part_end,  # Use the indicated part
                 '-c', 'copy',  # Don't re-encode, just copy
                 part_filename],
                check=True)
            fp.write("file '{}'\n".format(part_filename))

    # == Stitch/paste/concatenate together ===
    if len(parts) == 1:
        print('Renaming ...')
        os.rename(last_written, file_out)
    else:
        print('Concatenating ...')
        subprocess.run(
            ['ffmpeg',
             '-y',  # Overwrite silently
             '-loglevel', 'warning',  # Do print warnings, but no other "informative stuff"
             '-f', 'concat', '-i', list_filename,  # Concatenation instructions
             '-c', 'copy',  # Don't re-encode, just copy
             file_out],
            check=True)

    print('Result was written to {}'.format(file_out))


if __name__ == '__main__':
    exit_code = run(sys.argv[1:])
    exit(exit_code)