Maintain a lower-bitrate copy of a music library in sync with the main copy.

msync

Maintain a lower-bitrate copy of your music library, in sync with the main copy. Think of it as rsync, but only for music files, and with the ability to transcode high-bitrate or lossless files to lower-bitrate files suitable for use on devices with less storage.

It's also more opinionated than rsync, with behaviors tailored for exactly this use case. For example, msync will always remove files from the destination which are missing from the source; whereas rsync won't do this unless you pass it the --delete flag.

Use Cases

I use msync to keep a secondary, 160 Kbps AAC copy of my music library. This is synchronized occasionally to my iPhone, which lacks the space for a music library consisting of lossless and higher-bitrate files.

I accomplish this by adding a launchd job for msync, which runs nightly on the Mac Mini server whic hosts the music library.

Installation

Requirements: at the moment, msync supports only macOS. This is because it uses macOS's built-in afinfo tool to determine music files' bitrates.

make install will build msync for your current OS/architecture and install it to /usr/local/bin.

Usage

Basic usage is msync -from ~/Music -to ~/MusicSmaller -max-kbps 192, but you should review the available options as you'll likely want to use some of them.

Options

  • -ask-trash-permission: Trigger the macOS permission dialog for removing files immediately when the sync process begins (instead of later in the process, when we actually start removing files).
  • -dry-run: Don't actually modify anything on the filesystem, but print what would happen, including an estimate of the final size of the destination music library.
  • -file-mode: Octal value specifying mode for copied music files. Must begin with '0' or '0o'.
  • -from: Path of the source music library.
  • -max-kbps: Maximum bitrate, in Kbps, for the destination music library. Any music files of higher quality will be transcoded from the source library to the destination at this bitrate.
  • -remove-nonmusic-from-dest: Remove any non-music files from the destination, even if they are present in the source directory tree.
  • -symlink: For music files which are already under the maximum bitrate, create symlinks instead of actual copies. This is useful if you're mirroring your music library somewhere on the same machine, rather than directly to a portable device.
  • -to: Path of the destination music library.
  • -verbose: Log detailed output to stderr. Suppresses fancy progress indicators.
  • -version: Print version and exit.

Complete Usage Example

The complete invocation I use to maintain a 160Kbps mirror of my music library is:

msync -from "/Users/cdzombak/Music/iTunes/iTunes Media/Music" -to /Users/cdzombak/Music/160Kbps -max-kbps 160 -symlink -remove-nonmusic-from-dest -ask-trash-permission

Launch Agent

The file com.dzombak.music-160-mirror.plist in this repository is the Launch Agent I use. It runs the msync invocation listed above nightly at 2 AM.

About

Owner
Chris Dzombak
Chris Dzombak
https://github.com/cdzombak/msync
Comments
  • spinner results in a bunch of W chars

    spinner results in a bunch of W chars

    I don't know if this is because I appended an extremely long multiline text to the spinner, or because log output interrupted the spinner. Either way, fix it.

  • refactor

    refactor

    refactor, particularly main, to:

    • separate spinner & CLI concerns from program logic
    • make program logic less indenty
    • fix the myriad if verbose/dry run checks
    • log everything to stderr via log if verbose is selected
    • allow parallelizing transcoding and afinfo calls
  • show cursor even when aborted with ctrl-c

    show cursor even when aborted with ctrl-c

    capture SIGINT/SIGTERM (maybe SIGQUIT also) and make sure the spinner lib re-shows the cursor. this will be easier with a restructuring of main to separate core logic, program control flow, and spinner/status stuff.

  • parallelize afinfo calls & ffmpeg calls

    parallelize afinfo calls & ffmpeg calls

    The bulk of the time in scanning is spent in calling afinfo, and the bulk of the actual sync time is of course transcoding. Both of these could be parallelized easily, but it will require some restructuring: I'll need to separate the tree building/sync planning stages from the actual work, and the whole main function really needs some restructuring anyway.

  • Pick up on changed tags when determining what files to update

    Pick up on changed tags when determining what files to update

    For music under the limit, files are symlinked (if you use that option, anyway), which isn't a problem.

    But if files are copied or transcoded, and then the main copy's tags change (but not the name on disk), the copy/transcoded file is not updated.

  • allow customizing encoding approach

    allow customizing encoding approach

    rather than hardcoding ffmpeg, allow specifying eg. an encoding script that can call ffmpeg with whatever parameters you want. this also requires customizing the output file extension, since the program needs to know that to do sync-y things.

Related tags
Utilities music ffmpeg rsync
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