Running this extension currently fails with Mopidy >=4.0:

ERROR    2025-07-06 19:24:18,758 [658836:MainThread] mopidy.__main__
  Extension youtube failed during setup. This might have left the registry in a bad state.
Traceback (most recent call last):
  File "/home/blacklight/git_tree/mopidy/venv/lib/python3.13/site-packages/mopidy/__main__.py", line 158, in main
    extension.setup(registry)
    ~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/blacklight/git_tree/mopidy/venv/lib/python3.13/site-packages/mopidy_youtube/__init__.py", line 39, in setup
    from .backend import YouTubeBackend, YouTubeCoreListener
  File "/home/blacklight/git_tree/mopidy/venv/lib/python3.13/site-packages/mopidy_youtube/backend.py", line 10, in <module>
    from mopidy.models import Image, Ref, SearchResult, Track, model_json_decoder
ImportError: cannot import name 'model_json_decoder' from 'mopidy.models' (/home/blacklight/git_tree/mopidy/venv/lib/python3.13/site-packages/mopidy/models/__init__.py)

This is because of the changes in the Mopidy 4.0 models API:

Changes to the data models may affect any Mopidy extension or client.

• The models are now based on Pydantic data classes, which means:
  • All models fields and the replace() method should work as before, so
    unless your extension modifies or adds models, this should not affect you.
  • Models are now type-checked at runtime. This should help catch bugs early.
• Since we now use Pydantic to convert data models to and from JSON, the old
  model machinery has been removed. This includes the following:
  • :class:mopidy.models.ImmutableObject -- Not used by Mopidy since v1.0.5 nine
    years ago.
  • :class:mopidy.models.ValidatedImmutableObject -- The old base class for all models.
  • :class:mopidy.models.ModelJSONEncoder
  • :func:mopidy.models.model_json_decoder
  • :class:mopidy.models.fields.Collection
  • :class:mopidy.models.fields.Date
  • :class:mopidy.models.fields.Field
  • :class:mopidy.models.fields.Identifier
  • :class:mopidy.models.fields.Integer
  • :class:mopidy.models.fields.String
  • :class:mopidy.models.fields.URI