feat: mirror a lossless library to MP3 for iPod sync
Apple's Music app cannot read FLAC, so getting a lossless library onto an iPod requires a converted copy somewhere. This keeps that copy beside the library on a NAS rather than on a laptop, and keeps it current unattended. Walks a source tree and reproduces it path for path as MP3: tags and cover art carried across, already-MP3 sources copied rather than re-encoded, and mirror files whose source has gone deleted along with any directories they emptied. The source library is never written to. Freshness is tracked by modification time -- an encoded file is stamped with its source's mtime, so a file is stale exactly when the two differ. That keeps runs idempotent without a database that could fall out of step with whatever owns the library, which here is Lidarr. Encodes go to a temporary file and are renamed into place, so an interrupted run cannot leave a truncated MP3 that the next run mistakes for finished work. A lock file in the mirror root prevents overlapping passes. Ships as a Python package with a console script, a container image with a TrueNAS Scale compose file, and a Nix flake providing the package, an overlay and a dev shell. The test suite runs real ffmpeg encodes rather than mocks -- the failures worth catching are in what ffmpeg does with tags, cover art and container formats. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Emma Thorpe
co-authored by
Claude Opus 5
Claude Opus 5
parent
38f545ac32
commit
177761bb75
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import os
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import shutil
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import subprocess
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import sys
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import pytest
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# Ensure the project root is on sys.path when running tests.
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ROOT = os.path.dirname(os.path.dirname(__file__))
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if ROOT not in sys.path:
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sys.path.insert(0, ROOT)
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@pytest.fixture(scope="session", autouse=True)
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def require_ffmpeg():
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"""The tests exercise real encodes; there is little point faking them."""
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for tool in ("ffmpeg", "ffprobe"):
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if shutil.which(tool) is None:
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pytest.skip(f"{tool} is not on PATH", allow_module_level=True)
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@pytest.fixture
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def make_flac():
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"""Return a factory writing a short tagged FLAC file."""
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def factory(path, title="Test Title", artist="Test Artist", album="Test Album", seconds=1):
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path.parent.mkdir(parents=True, exist_ok=True)
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subprocess.run(
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[
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"ffmpeg",
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"-nostdin",
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"-hide_banner",
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"-loglevel",
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"error",
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"-y",
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"-f",
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"lavfi",
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"-i",
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f"sine=frequency=440:duration={seconds}",
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"-metadata",
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f"title={title}",
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"-metadata",
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f"artist={artist}",
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"-metadata",
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f"album={album}",
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"-metadata",
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"track=3",
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str(path),
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],
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check=True,
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capture_output=True,
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)
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return path
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return factory
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@pytest.fixture
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def probe_tag():
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"""Return a helper reading a single metadata tag from a file."""
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def reader(path, tag):
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completed = subprocess.run(
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[
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"ffprobe",
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"-v",
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"error",
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"-show_entries",
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f"format_tags={tag}",
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"-of",
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"default=noprint_wrappers=1:nokey=1",
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str(path),
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],
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check=True,
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capture_output=True,
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text=True,
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)
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return completed.stdout.strip()
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return reader
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@@ -0,0 +1,228 @@
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import os
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import subprocess
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import time
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import pytest
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import music_mirror
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def run(source, mirror, *extra):
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return music_mirror.main(["--source", str(source), "--mirror", str(mirror), *extra])
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def test_parse_quality_accepts_vbr_and_cbr():
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assert music_mirror.parse_quality("V0") == ["-q:a", "0"]
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assert music_mirror.parse_quality("v2") == ["-q:a", "2"]
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assert music_mirror.parse_quality("256") == ["-b:a", "256k"]
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def test_parse_quality_rejects_nonsense():
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with pytest.raises(ValueError):
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music_mirror.parse_quality("best")
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def test_parse_interval_units():
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assert music_mirror.parse_interval("90") == 90
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assert music_mirror.parse_interval("30m") == 1800
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assert music_mirror.parse_interval("6h") == 21600
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assert music_mirror.parse_interval("1d") == 86400
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def test_encodes_and_preserves_layout_and_tags(tmp_path, make_flac, probe_tag):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "Test Artist" / "Test Album" / "03 Song.flac")
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assert run(source, mirror) == 0
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output = mirror / "Test Artist" / "Test Album" / "03 Song.mp3"
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assert output.is_file()
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assert probe_tag(output, "title") == "Test Title"
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assert probe_tag(output, "album") == "Test Album"
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def test_output_is_mp3(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "a.flac")
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run(source, mirror)
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codec = subprocess.run(
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[
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"ffprobe",
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"-v",
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"error",
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"-select_streams",
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"a:0",
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"-show_entries",
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"stream=codec_name",
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"-of",
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"csv=p=0",
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str(mirror / "a.mp3"),
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],
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check=True,
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capture_output=True,
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text=True,
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).stdout.strip()
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assert codec == "mp3"
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def test_second_pass_skips_unchanged_files(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "a.flac")
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run(source, mirror)
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first = (mirror / "a.mp3").stat().st_mtime_ns
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run(source, mirror)
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assert (mirror / "a.mp3").stat().st_mtime_ns == first
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def test_changed_source_is_re_encoded(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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track = make_flac(source / "a.flac")
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run(source, mirror)
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before = (mirror / "a.mp3").stat().st_mtime
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# A replaced file with a newer mtime is what a Lidarr quality upgrade
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# looks like on disk.
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later = time.time() + 120
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os.utime(track, (later, later))
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run(source, mirror)
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assert (mirror / "a.mp3").stat().st_mtime > before
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def test_deleted_source_is_pruned(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "Album" / "a.flac")
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make_flac(source / "Album" / "b.flac")
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run(source, mirror)
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(source / "Album" / "b.flac").unlink()
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run(source, mirror)
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assert (mirror / "Album" / "a.mp3").is_file()
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assert not (mirror / "Album" / "b.mp3").exists()
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def test_emptied_directory_is_removed(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "Gone" / "a.flac")
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run(source, mirror)
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(source / "Gone" / "a.flac").unlink()
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run(source, mirror)
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assert not (mirror / "Gone").exists()
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def test_no_prune_keeps_orphans(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "a.flac")
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run(source, mirror)
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(source / "a.flac").unlink()
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run(source, mirror, "--no-prune")
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assert (mirror / "a.mp3").is_file()
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def test_existing_mp3_is_copied_not_re_encoded(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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flac = make_flac(source / "a.flac")
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subprocess.run(
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["ffmpeg", "-loglevel", "error", "-y", "-i", str(flac), str(source / "b.mp3")],
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check=True,
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capture_output=True,
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)
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flac.unlink()
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run(source, mirror)
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assert (mirror / "b.mp3").read_bytes() == (source / "b.mp3").read_bytes()
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def test_dry_run_writes_nothing(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "a.flac")
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assert run(source, mirror, "--dry-run") == 0
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assert not (mirror / "a.mp3").exists()
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def test_subdir_limits_the_pass_and_does_not_prune(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "One" / "a.flac")
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make_flac(source / "Two" / "b.flac")
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assert run(source, mirror, "--subdir", "One") == 0
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assert (mirror / "One" / "a.mp3").is_file()
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# Outside the requested directory: neither encoded nor treated as an orphan.
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assert not (mirror / "Two").exists()
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def test_external_cover_is_embedded(tmp_path, make_flac):
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source = tmp_path / "src"
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mirror = tmp_path / "dst"
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make_flac(source / "Album" / "a.flac")
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subprocess.run(
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[
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"ffmpeg",
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"-loglevel",
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"error",
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"-y",
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"-f",
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"lavfi",
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"-i",
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"color=c=red:s=64x64:d=1",
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"-frames:v",
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"1",
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str(source / "Album" / "cover.jpg"),
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],
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check=True,
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capture_output=True,
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)
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run(source, mirror)
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streams = subprocess.run(
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[
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"ffprobe",
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"-v",
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"error",
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"-select_streams",
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"v",
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"-show_entries",
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"stream=codec_name",
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"-of",
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"csv=p=0",
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str(mirror / "Album" / "a.mp3"),
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],
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check=True,
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capture_output=True,
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text=True,
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).stdout.strip()
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assert streams # a picture stream is present
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def test_mirror_inside_source_is_refused(tmp_path, make_flac):
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source = tmp_path / "src"
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make_flac(source / "a.flac")
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assert run(source, source / "mp3") == 2
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def test_missing_source_is_refused(tmp_path):
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assert run(tmp_path / "nope", tmp_path / "dst") == 2
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