Can't Export Timeline with FCPX adapter (AttributeError: 'NoneType' object has no attribute 'get')

[philipph77]

I am trying to export a minimal timeline (only one audio track) with the fcpx_xml adapter, and open the timeline in Final Cut Pro X.
Exporting this timeline without adapters works without any problems. However, when using the fcpx_xml adater it raises an error.

Here is a minimal code example written in python and the stack trace:

import os
from pathlib import Path
from zipfile import ZipFile

from hachoir.parser import createParser
from hachoir.metadata import extractMetadata
import opentimelineio as otio


def write_zipfile(archive_name: str, timeline_file: Path, songfile: Path, clip_files: list[str], logdir: str) -> None:
    # writes the timeline_file together with the songfile and clip_files into one zip archive
    with ZipFile(archive_name, "w") as archive:
        for clip_file in clip_files: 
            archive.write(os.path.join(logdir, clip_file), os.path.join("media",clip_file))
        archive.write(os.path.join(timeline_file), timeline_file.name)
        archive.write(songfile, os.path.join("media",songfile.name))

def get_song_duration(songfile_path: Path):
    # returns the duration of the songfile in seconds
    song_parser = createParser(str(songfile_path.resolve()))
    song_metadata = extractMetadata(song_parser)
    return song_metadata.get("duration").total_seconds()

def main(songfile_path: Path):
    # create the timeline and track objects
    tl = otio.schema.Timeline(name="Storyline")
    tr_audio = otio.schema.Track(name="Audio", kind=otio.schema.Track.Kind.Audio)
    tl.tracks.append(tr_audio)

    # create the audio clip and append to the audio track
    song_duration = get_song_duration(songfile_path)
    cl_audio = otio.schema.Clip(
        name=str(songfile_path.stem),
        media_reference=otio.schema.ExternalReference(
            target_url="media/"+str(songfile_path.name),
            available_range=otio.opentime.TimeRange(
                start_time=otio.opentime.RationalTime(0, 1),
                duration=otio.opentime.RationalTime(song_duration, 1),
            )
        ),
        source_range=otio.opentime.TimeRange(
            start_time=otio.opentime.RationalTime(0, 1),
            duration=otio.opentime.RationalTime(song_duration, 1),
        )
    )
    tr_audio.append(cl_audio)

    # export timeline with fcpx_adapter
    fcp_xml_timeline_file = "timeline.fcpxml"
    otio.adapters.write_to_file(tl, fcp_xml_timeline_file, adapter_name="fcpx_xml")
    archive_name = "timeline_fcpx_xml.zip"
    write_zipfile(archive_name, Path(fcp_xml_timeline_file), songfile_path, [], "")

Traceback (most recent call last):
  File "/Users/FPJ21JY/Documents/Videographer/playground_fcpxml_adapter.py", line 60, in <module>
    main(songfile_path)
  File "/Users/FPJ21JY/Documents/Videographer/playground_fcpxml_adapter.py", line 50, in main
    otio.adapters.write_to_file(tl, fcp_xml_timeline_file, adapter_name="fcpx_xml")
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio/adapters/__init__.py", line 192, in write_to_file
    return adapter.write_to_file(
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio/adapters/adapter.py", line 192, in write_to_file
    result = self.write_to_string(input_otio, **adapter_argument_map)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio/adapters/adapter.py", line 283, in write_to_string
    return self._execute_function(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio/plugins/python_plugin.py", line 153, in _execute_function
    return (getattr(self.module(), func_name)(**kwargs))
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio_contrib/adapters/fcpx_xml.py", line 1161, in write_to_string
    return FcpxOtio(input_otio).to_xml()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio_contrib/adapters/fcpx_xml.py", line 172, in to_xml
    top_sequence = self._stack_to_sequence(project.tracks)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio_contrib/adapters/fcpx_xml.py", line 248, in _stack_to_sequence
    self._track_for_spine(track, lane_id, spine, compound_clip)
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio_contrib/adapters/fcpx_xml.py", line 271, in _track_for_spine
    offset = self._offset_based_on_parent(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/FPJ21JY/anaconda3/envs/videographer/lib/python3.11/site-packages/opentimelineio_contrib/adapters/fcpx_xml.py", line 309, in _offset_based_on_parent
    parent.get("offset"),
    ^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'get'