Play an uploaded library song

A song the user uploaded to their library has no Apple Music catalog counterpart. Apple returns it as a library-songs resource without playParams.catalogId, and MusicKit plays it from a raw audio file instead of a DRM stream. The mock models it as UploadedLibrarySong in mock.data.library_songs and WebPlaybackUploadedLibrarySong in mock.endpoints.web_playback.

Register the song and its audio

from musickit_api_mock import MusicKitApiMock, UploadedLibrarySong

mock = MusicKitApiMock()

song = UploadedLibrarySong.from_file("path/to/upload.m4a")
song.artist_name = "Me"

mock.data.library_songs = {"i.abc123": song}

from_file reads the file the way a Music.app import does — title, artist, album, genre, track / disc numbers, duration, and embedded artwork — and transcodes the audio to AAC in an M4A container, as Apple does for uploads. A file with missing tags yields the same attributes Apple emits for such an upload. To model edits made in Music.app after the import, assign to the returned song's fields.

Answer the web-playback request

When MusicKit plays the song it posts {"universalLibraryId": "i.abc123"} to the web-playback endpoint, so key the setter by the library id and point the asset at a blobstore.apple.com URL whose second path segment is the library id:

from musickit_api_mock import (
    WebPlaybackResponseSuccess,
    WebPlaybackUploadedLibraryAsset,
    WebPlaybackUploadedLibraryAssetMetadata,
    WebPlaybackUploadedLibrarySong,
)

mock.endpoints.web_playback = {
    "i.abc123": WebPlaybackResponseSuccess(
        song_list=[
            WebPlaybackUploadedLibrarySong(
                asset=WebPlaybackUploadedLibraryAsset(
                    url="https://store-001.blobstore.apple.com/uploads/i.abc123/audio",
                    metadata=WebPlaybackUploadedLibraryAssetMetadata(
                        item_name="Home Recording",
                        artist_name="Me",
                        playlist_name="Demos",
                        duration=128_373,
                        kind="song",
                    ),
                ),
            )
        ]
    ),
}

The mock serves https://<store>.blobstore.apple.com/<bucket>/<library song id>/audio from the registered song's audio with Content-Type: audio/x-m4a; the store label and bucket segment are free-form, and a signing query string is ignored.