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Recursively mirror a directory tree of FLAC audio files to AAC or OGG.
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Latest commit fe95e74 Oct 13, 2014 @cmcginty Merge pull request #7 from rslomkow/master
Added support for flac embedded album art.
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LICENSE [build] Update Makefile for Sphinx and tool-chain changes Jun 16, 2011


Recursively mirror a directory tree of FLAC audio files to AAC/OGG/MP3. Source files can be filtered (by sub-directory, or full path) in order to limit the files converted. The script will also attempt to retain all meta-data fields in the output files.

At a Glance

  • Mirror directory tree of FLAC files audio files to AAC/OGG/MP3 (re-encoded using NeroAacEnc, oggenc, or LAME).
  • Filter source tree using one or more sub-directory paths.
  • By default, will only re-encode missing or out-of-date AAC/OGG/MP3 files.
  • Optionally deletes orphaned output files.
  • Multi-threaded encoding ensures full CPU utilization.
  • Supports transfer of FLAC meta-data including title, artist, album.
  • Converts FLAC replaygain field to Apple iTunes Sound Check.
  • Optionally resizes and embeds album cover art JPEG files to destination files.
  • Optionally copy cover art to destination directories.

Usage Model

  • Hard disk space is cheap, but flash-based media players are still limited in capacity.
  • Create a lossy encoded "mirror" of your music files for portability.
  • Setup a daily cron job to always keep your FLAC and AAC/OGG files synchronized.
  • Re-encode your FLAC library to different AAC/OGG bit-rates in one command.

Running and Options

Flacsync is run from the command-line, using the following format.

flacsync [options] BASE_DIR [SOURCE ...]


Define the root path of a directory hierarchy containing desired input files (FLAC). A mirrored output directory will be created in the deepest path, parallel to BASE_DIR, and named after the selected output file extension.

For example, if BASE_DIR is /data/flac, the output dir will be /data/aac.


Optional dir/file argument list to select source files for transcoding. If not defined, all files in BASE_DIR will be transcoded. The SOURCE file/dir list must be relative from BASE_DIR or the current working directory.

--version show program's version number and exit
-h, --help show this help message and exit
 set max number of encoding threads [default:2]
-f, --force force re-encode of all files from the source dir; by default source files will be skipped if it is determined that an up-to-date copy exists in the destination path
-t ENC_TYPE, --type=ENC_TYPE
 select the output transcode format; supported values are 'aac','ogg','mp3' [default:aac]
-o, --ignore-orphans
 prevent the removal of files and directories in the dest dir that have no corresponding source file
-d DEST_DIR, --destination=DEST_DIR
 define alternate destination output directory to override the default. The standard default destination directory will be created in the same parent directory of BASE_DIR. See BASE_DIR above.
-r, --resize enable resizing of cover art; by default the art that is found will be saved to file without resizing.
-j, --copy-cover-art
 in addition to embedding cover art, copy image file directly to the desination sub-folder.

AAC Encoder Options:

-q AAC_Q, --aac-quality=AAC_Q
 set the AAC encoder quality value, must be a float range of 0..1 [default:0.35]

OGG Encoder Options:

-g OGG_Q, --ogg-quality=OGG_Q
 set the Ogg Vorbis encoder quality value, must be a float range of -1..10 [default:5]

MP3 Encoder Options:

-m MP3_Q, --mp3-quality=MP3_Q
 set the Lame MP3 encoder quality value, must be a initeger range of 0..9 [default:3]


  1. Encode a directory of FLAC files to AAC. Output file will be written to /music/aac.

    flacsync /music/flac
    cd /music/flac; flacsync .
  2. Encode a directory of FLAC files to AAC. Output files will be written to /ipod.

    flacsync -d /ipod /music/flac
  3. Encode a directory of FLAC files to high-quality OGG, using 4 CPU threads.

    flacsync -c 4 -t ogg -g 9 /music/flac
  4. Force re-encode two albums of FLAC files, even if the AAC files exist.

    flacsync -f /music/flac artist1/album artist2/album
    cd /music/flac; flacsync -f . artist1/album artist2/album
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