Mux Youtube DASH audio and video

mux.py

from __future__ import unicode_literals

import sys

from sh import ffmpeg
from unipath import Path

_, src_dir, dest_dir = sys.argv

src_dir = Path(src_dir)
dest_dir = Path(dest_dir)

if not dest_dir.exists():
    dest_dir.mkdir()

m4a = set(f.stem for f in src_dir.listdir('*.m4a'))
mp4 = set(f.stem for f in src_dir.listdir('*.mp4'))

both = sorted(m4a & mp4)

for basename in both:
    source_video = src_dir + basename + '.mp4'
    source_audio = src_dir + basename + '.m4a'
    destination = dest_dir + basename + '.480.mp4'

    if source_audio.exists() and source_video.exists():
        if destination.exists():
            print destination, 'already muxed!'
        else:
            print destination, 'running ffmpeg...'
            ffmpeg(
                '-i', source_video,
                '-i', source_audio,
                '-vcodec', 'copy',
                '-acodec', 'copy',
                destination,
            )
            print 'OK'