Emma ThorpeandClaude Opus 5
cbcbf30228
Build and publish container / build (pull_request) Canceled after 14m59s
The deployment target is a container on TrueNAS Scale, so the flake sat on no path between the source and the NAS. It was carried over from a sibling project where the flake is the deployment mechanism; here it only added a second build path and a second dependency pin. Worse, it tested the wrong thing: `nix flake check` ran the suite against nixpkgs' ffmpeg while the shipped artefact contains Debian's, and encoder and muxer behaviour is exactly what these tests cover. The Dockerfile gains a `test` stage that installs pytest and runs the suite against the image's own ffmpeg; a failing test fails the build. CI runs `docker build --target test` in place of the host-based Python setup, and the push build states `target: runtime` so the published image is the lean stage rather than the last one in the file. The runtime image carries neither the tests nor pytest. The release step now calls python3 rather than python, since setup-python is no longer in the job to provide the alias. Removes package.nix, flake.nix and flake.lock. A dev shell is a `nix shell` away for anyone who wants one, and the README says so. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
144 lines
7.3 KiB
Markdown
144 lines
7.3 KiB
Markdown
# music-mirror
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Maintain a lossy MP3 mirror of a lossless music library.
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Walks a source library and reproduces it, path for path, as MP3 in a separate
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tree. Tags and cover art are carried across; sources that are already MP3 are
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copied rather than re-encoded; mirror files whose source has been deleted are
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removed. **The source library is never written to** — it is mounted read-only
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in the supplied compose file, and nothing in the code opens it for writing.
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The intended use is an iPod. Apple's Music app cannot read FLAC at all, so a
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converted copy has to exist somewhere; this keeps that copy next to the
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library on a NAS instead of on a laptop, and keeps it current without a human
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remembering to do anything.
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## How it decides what to do
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| Situation | Action |
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| -------------------------------- | ---------------------------------------- |
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| No mirror file | encode |
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| Source modified since the mirror | re-encode (a Lidarr quality upgrade) |
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| Mirror up to date | skip |
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| Source is already MP3 | copy verbatim |
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| Source gone | delete the mirror file, prune empty dirs |
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Freshness is modification time: an encoded file is stamped with its source's
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mtime, so a file is stale exactly when the two differ. There is no database to
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fall out of step with the library, which matters when something else — Lidarr,
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in this case — is the thing that owns and reorganises it.
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### What that means for Lidarr
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| Lidarr does this | The mirror does this |
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| --------------------------------------- | -------------------------------------------------------------------------------- |
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| Replaces a file with a better rip | Re-encodes in place. Same path in, same path out, so no duplicate |
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| Upgrades MP3 to FLAC | Both map to the same `.mp3` mirror path, so the old one is overwritten |
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| Renames a track, album or artist folder | Old path pruned, new path encoded. Correct, but it re-encodes rather than moving |
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| Deletes an album or artist | Every orphaned mirror file is deleted and the emptied directories go too |
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Pruning is driven by what the pass actually found, not by guessing source
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filenames from mirror ones: a `.FLAC` source would not be found by a search for
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`.flac`, and the mirror file would be deleted and rebuilt on alternate passes
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for ever.
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If two sources want the same mirror path — a `01 Song.flac` next to a leftover
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`01 Song.mp3`, which is what an interrupted upgrade leaves — the better format
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wins, ties break on path, and the loser is logged. Without that rule both
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encode to the same destination and every pass finds one of them stale.
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The mtime is read _before_ encoding rather than after. A file still being
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written when the pass reaches it would otherwise be stamped with its final
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mtime while holding truncated audio, and never be revisited.
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Encodes are written to a temporary file and renamed into place, so an
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interrupted run cannot leave a truncated MP3 that the next run mistakes for
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finished work. A lock file in the mirror root stops two passes overlapping.
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## Usage
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```sh
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music-mirror --source /music --mirror /music-mp3 # one pass
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music-mirror --source /music --mirror /music-mp3 --interval 6h # keep running
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music-mirror --source /music --mirror /music-mp3 --dry-run # report only
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music-mirror --source /music --mirror /music-mp3 --subdir "Artist/Album"
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```
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| Option | Environment variable | Default | Meaning |
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| ------------ | ----------------------- | --------- | ---------------------------------------------- |
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| `--source` | `MUSIC_MIRROR_SOURCE` | — | Root of the lossless library, read-only |
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| `--mirror` | `MUSIC_MIRROR_MIRROR` | — | Root of the MP3 mirror |
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| `--quality` | `MUSIC_MIRROR_QUALITY` | `V0` | LAME VBR level `V0`–`V9`, or kbps e.g. `256` |
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| `--jobs` | `MUSIC_MIRROR_JOBS` | CPU count | Concurrent encodes |
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| `--interval` | `MUSIC_MIRROR_INTERVAL` | unset | Repeat forever, e.g. `45m`, `6h`, `1d` |
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| `--subdir` | — | unset | Limit the pass to one directory; skips pruning |
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| `--no-prune` | — | off | Keep mirror files whose source has gone |
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| `--dry-run` | — | off | Report what would change, write nothing |
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`--subdir` never prunes: a partial pass cannot tell an orphan from a file
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outside its own scope.
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Requires `ffmpeg` and `ffprobe` on `PATH`. The container image provides both.
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## Running it on TrueNAS Scale
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`compose.yaml` is a Custom App definition. Adjust the two host paths and the
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`user:` to match your pool, then add it as a custom app. The image is published
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to this Gitea's registry on every release:
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```
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code.emmathe.dev/lyrathorpe/music-mirror:latest
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```
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Tags are `latest`, the full version, and the truncated `major.minor` and
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`major` forms; builds that are not releases are published as `sha-<short>`.
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Point the mirror at its own dataset rather than a directory inside the music
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dataset — it is derived data, so it wants its own snapshot policy, its own
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quota, and its own SMB share. The tool refuses to run with a mirror inside the
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source tree.
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New Lidarr imports are picked up on the next pass. With `MUSIC_MIRROR_INTERVAL`
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at `6h` that is the worst case; run `--subdir` by hand if you want an album
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immediately.
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## Tests
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```sh
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docker build --target test . # what CI runs
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pytest # needs ffmpeg and pytest on PATH
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```
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The suite runs real ffmpeg encodes rather than mocking them. The interesting
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failures are in what ffmpeg actually does with tags, cover art and container
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formats, and a mock cannot fail that way — which is also why CI runs the tests
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_inside the image_, against the ffmpeg that ships, rather than against whatever
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the build runner provides. The published image is the `runtime` stage and
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carries neither the tests nor pytest.
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Run them directly instead if you prefer; they skip when ffmpeg is absent. On a
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Nix machine:
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```sh
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nix shell nixpkgs#python3Packages.pytest nixpkgs#ffmpeg -c pytest
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```
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## Getting the result onto an iPod
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The mirror is just a directory of MP3s, so any client will do:
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- **macOS.** Add the mirror's SMB share to the Music app with _Copy files to
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Music Media folder_ and _Keep Media folder organised_ both **off**. The Mac
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then stores a library database and nothing else. Keep the share mounted at a
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stable path — if it is missing when Music opens, every track shows `!`.
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- **Linux.** Rhythmbox links `libgpod` and handles iPod sync. An iPod Video
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(5th generation) predates the models whose database has to be signed, so no
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firmware-hash trickery is needed.
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Neither client transcodes at sync time; they copy finished MP3s.
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Two device-side details worth knowing: the iPod reads cover art from the file's
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tags and ignores `folder.jpg`, which is why art is embedded here; and volume
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levelling on the device uses iTunes' Soundcheck tag, not ReplayGain, so
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ReplayGain tags in the source are not carried over as such.
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