Generate crazy MP4 edit lists to be added to media files for testing.

gen-edit-lists.py

#!/usr/bin/python3
#
# Generate crazy MP4 edit lists to be added to media files for testing.
#
# 1. Modify the timescales below with the actual values from the MP4 file.
#
# 2. Run the following commands to patch the file with Bento:
#
#    # Remove previously existing edit list (optional, only if there is some)
#    mp4edit --remove moov/trak/edts original.mp4 patched1.mp4
#    # Generate the new ones
#    python gen-edit-lists.py
#    # Insert the new edit lists
#    mp4edit --insert moov/trak[0]:edts_video.box:-1 patched{1,2}.mp4
#    mp4edit --insert moov/trak[1]:edts_audio.box:-1 patched{2,3}.mp4
#
import struct
from collections import namedtuple

Edit = namedtuple("Edit", ["duration", "media_time", "media_rate"])

movie_timescale = 600
video_track_timescale = 24000
audio_track_timescale = 48000


def gen_desired_edits(track_timescale):
    return [
        # First 5 seconds of the movie consist of the track media from
        # [4, 4+5) s.
        Edit(5 * movie_timescale, 4 * track_timescale, 1),
        # The following 90 seconds of the movie consist of the track media from
        # [40, 40+90) s.
        Edit(90 * movie_timescale, 40 * track_timescale, 1),
        # The following 20 seconds in the movie, there is nothing.
        Edit(20 * movie_timescale, -1, 1),
        # Then, 10 seconds of video from the beginning of the track
        Edit(10 * movie_timescale, 0 * track_timescale, 1),
        # Then, 5 seconds of still image from the second 1 of the track
        Edit(5 * movie_timescale, 1 * track_timescale, 0),
    ]


def gen_elst(desired_edits):
    flags = 0
    version = 1 if any(
        edit.duration > 0xFFFFFFFF or edit.media_time > 0xFFFFFFFF
        for edit in desired_edits
    ) else 0

    contents = struct.pack(">LL", (version << 24) | flags, len(desired_edits))
    for edit in desired_edits:
        if version == 1:
            contents += struct.pack(">Qq", edit.duration, edit.media_time)
        else:
            contents += struct.pack(">Ll", edit.duration, edit.media_time)
        contents += struct.pack(">hh", edit.media_rate, 0)

    # Write the header
    return struct.pack(">L", 8 + len(contents)) + b"elst" + contents


def gen_edts(desired_edits):
    elst = gen_elst(desired_edits)
    return struct.pack(">L", 8 + len(elst)) + b"edts" + elst


if __name__ == '__main__':
    with open("edts_audio.box", "wb") as f:
        f.write(gen_edts(gen_desired_edits(audio_track_timescale)))

    with open("edts_video.box", "wb") as f:
        f.write(gen_edts(gen_desired_edits(video_track_timescale)))