a codification of a particular method of using ffmpeg to clean up certain FLVs.

ffmpeg_crop.sh

# cropping mp4 video in ffmpeg. 
#
# this does require a re-encode but the following process created video 
# half the size with no perceptible change in quality. audio is unaffected.

# detect area to crop
ffplay -i show.mp4 -vf "cropdetect=24:16:0"

# crop to 944x720, x-offset=170, y-offset=0 (removing vertical black bars)
ffmpeg -i show.mp4 -vf "crop=944:720:170:0" show_cropped.mp4

# do that in a loop for five shows
for i in $(seq 1 5); do ffmpeg -i show_10${i}.mp4 -vf "crop=944:720:170:0" show_10${i}_cropped.mp4; done

# NOTE: "-strict -2" may be necessary depending on your ffmpeg's codec support. 

flv2mp4.py

"""
Translates MP4-encoded FLVs to native MP4 and then concatenates
them. It is up to the encoder to ensure that the original FLVs 
actually contain MP4. Expects ffmpeg to be installed. No python 
requirements.

Usage:

python flv2mp4.py --output ../show.mp4 *.flv

Relevant commands for easy reference:

# switches from an FLV container to a native MP4 container without reencoding
ffmpeg -i show_1.flv -codec show_1.mp4

# concatenates the mp4s listed in file_list.txt without reencoding.
ffmpeg -f concat -i file_list.txt -c copy show_joined.mp4
"""

import os
import shutil
import argparse
import subprocess

def parse_args():
    prs = argparse.ArgumentParser()
    prs.add_argument('input_files', nargs='+')
    prs.add_argument('--output')
    prs.add_argument('--overwrite', action='store_true')
    return prs.parse_args()


def mkdir_p(path):
    try:
        os.makedirs(path)
    except OSError as exc:
        if exc.errno == errno.EEXIST and os.path.isdir(path):
            return
        raise
    return


def convert_flv(flv_path, dest_path, overwrite=False):
    if os.path.isdir(dest_path):
        dest_fn = os.path.splitext(os.path.split(flv_path)[1])[0] + '.mp4'
        dest_path = os.path.join(dest_path, dest_fn)
    print ' - writing to destination path:', dest_path
    command = ['ffmpeg']
    if overwrite:
        command.append('-y')
    else:
        command.append('-n')
    command.extend(['-i', flv_path, '-codec',  'copy', dest_path])
    print command
    output = subprocess.check_output(command)
    return dest_path


def concat_mp4s(mp4_list, output_path, scratch_path, overwrite=False):
    file_list_path = make_file_list(mp4_list, scratch_path)
    command = ['ffmpeg', '-f', 'concat', '-i', file_list_path, '-c', 'copy']
    if overwrite:
        command.append('-y')
    else:
        command.append('-n')
    command.append(output_path)
    print command
    output = subprocess.check_output(command)
    print output
    return output


def make_file_list(mp4_list, scratch_path):
    lines = []
    for mp4_path in mp4_list:
        lines.append("file '%s'" % mp4_path.replace("'", r"\'"))
    file_list_path = os.path.join(scratch_path, 'file_list.txt')
    with open(file_list_path, 'w') as f:
        f.write('\n'.join(lines))
    return file_list_path


def make_output_fn(input_fns):
    output_fn = os.path.splitext(input_fns[0])[0] + '.mp4'
    if len(input_fns) > 1:
        output_fn = os.path.commonprefix(input_fns).strip() + '_joined.mp4'
    return output_fn


def main():
    args = parse_args()
    input_fns = args.input_files
    output_fn = args.output
    overwrite = args.overwrite
    cur_path = os.path.abspath('.')
    if not output_fn:
        output_dir = cur_path
        output_fn = make_output_fn(input_fns)
    elif os.path.isdir(output_fn):
        output_dir = output_fn
        output_fn = make_output_fn(input_fns)
    else:
        output_dir, output_fn = os.path.split(output_fn)
        output_dir = output_dir or cur_path
    output_path = os.path.abspath(os.path.join(output_dir, output_fn))
    scratch_dir = os.path.join(output_dir, 'tmpflvconv')

    mkdir_p(scratch_dir)  # TODO: mkdtemp?

    try:
        mp4_list = []
        for fn in input_fns:
            mp4_path = convert_flv(fn, scratch_dir, overwrite=overwrite)
            mp4_list.append(mp4_path)
        concat_mp4s(mp4_list, output_path, scratch_dir, overwrite=overwrite)
        print 'output mp4 successfully written to', output_path
    finally:
        shutil.rmtree(scratch_dir)


if __name__ == '__main__':
    main()