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FUSE-based transcoding filesystem from FLAC to MP3
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mp3fs is a read-only FUSE filesystem which transcodes between audio formats (currently FLAC and Ogg Vorbis to MP3) on the fly when opened and read.

This can let you use a FLAC or Ogg Vorbis collection with software and/or hardware which only understands the MP3 format, or transcode files through simple drag-and-drop in a file browser.

For installation instructions see the install file.


Mount your filesystem like this:

mp3fs [-b bitrate] musicdir mountpoint [-o fuse_options]

For example,

mp3fs -b 128 /mnt/music /mnt/mp3 -o allow_other,ro

In recent versions of FUSE and mp3fs, the same can be achieved with the following entry in /etc/fstab:

mp3fs#/mnt/music /mnt/mp3 fuse allow_other,ro,bitrate=128 0 0

At this point the files /mnt/music/**.flac and /mnt/music/**.ogg will show up as /mnt/mp3/**.mp3.

How it Works

When a file is opened, the decoder and encoder are initialised and the file metadata is read. At this time the final filesize can be determined as we only support constant bitrate (CBR) MP3 files.

As the file is read, it is transcoded into an internal per-file buffer. This buffer continues to grow while the file is being read until the whole file is transcoded in memory. The memory is freed only when the file is closed. This simplifies the implementation.

Seeking within a file will cause the file to be transcoded up to the seek point (if not already done). This is not usually a problem since most programs will read a file from start to finish. Future enhancements may provide true random seeking.

ID3 version 2.4 and 1.1 tags are created from the vorbis comments in the FLAC or Ogg Vorbis file. They are located at the start and end of the file respectively.

A special optimisation is made so that applications which scan for id3v1 tags do not have to wait for the whole file to be transcoded before reading the tag. This dramatically speeds up such applications.


mp3fs uses Git for revision control. You can obtain the full repository with:

git clone

mp3fs is written in a mixture of C and C++ and uses the following libraries:


This program is maintained by K. Henriksson, who is the primary author from 2008 to present.

The original maintainer and author was David Collett from 2006 to 2008. Much thanks to him for his original work.


This program can be distributed under the terms of the GNU GPL version 3 or later. It can be found online or in the COPYING file.

This file and other documentation files can be distributed under the terms of the GNU Free Documentation License 1.3 or later. It can be found online or in the COPYING.DOC file.

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