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gcc 8.2.0 FFmpeg 4.1.4 Build Status
clang 7.0.1 FFmpeg 4.1.4 Build Status


Planned features

  • Issue #63: Interesting feature request - hardware support for encoding and decoding. Experimental hardware acceleration support has been added. If you feel lucky do "git checkout FB" and try it out.
  • Currently I am preparing a Windows version, but this is going to take some time. I need to port the Fuse functionality to Windows which is quite a huge project in itself.

New in 2.1:

  • Feature: Add BLURAY_VIDEO_FORMAT_2160P (UHD)
  • Bugfix: Did not transcode some source files with invalid DTS.
  • Bugfix: Cosmetical - No need to log date/time twice in syslog.
  • Bugfix: Cosmetical - Fix man page/online help for --recodesame parameter.
  • Log cache close action at trace level
  • Shorter log entry when opening cache files

Version 2.0 released

Finally. we are at 2.0!

New in 2.0:

  • Feature: No new features, new release 2.0 after feature freeze.
  • Bugfix: Issue #64 - Fixed playback stopping prematurely on some files.


Web site:

FFmpegfs is a read-only FUSE filesystem which transcodes between audio and video formats on the fly when opened and read.

Supported output formats:

Format Description Video Audio
WebM VP9 Opus
OGG Theora
MOV QuickTime File Format H264 AAC
Prores Prores AAC
Opus Opus
MP3 MPEG-2 Audio Layer III MP3
WAV Waveform Audio File Format PCM 16 bit LE
AIFF Audio Interchange File Format PCM 16 bit BE
ALAC Apple Lossless Audio Codec ALAC
JPG Video to frameset JPEG
PNG Video to frameset PNG
BMP Video to frameset BMP
TS MPEG transport stream H264 AAC
HLS HTTP Live Streaming H264 AAC

This can let you use a multi media file collection with software and/or hardware which only understands one of the supported output formats, or transcode files through simple drag-and-drop in a file browser.

For live streaming select WebM or MP4 for best results. If video transcoding is not required MP3 will also do, but WebM and MP4 will create better results. The OGG encoder is not fast enough for real-time recoding files.

When a destination JPG, PNG or BMP is chosen, all frames of a video source file will be presented in a virtual directory named after the source file. Audio will not be available.

Selecting HLS creates a directory with TS segments together with a M3U playlist (index_0_av.m3u8 and master.m3u8). There is also a hls.html that can be opened in a browser to play the segments.

Please note that the files must be on a webserver because restrictions prevent most browsers from opening the files from disk. See FIXING PROBLEMS for details.

Installation Instructions

Supported Linux Distributions

Tested with:

Distribution FFmpeg Version Remarks Result
Daily build N-97739-g876cfa67f3 OK!
Debian 9 Stretch 3.2.8-1~deb9u1 OK!
Debian 10 Buster 3.2.14-1~deb9u1 OK!
Debian 11 Bullseye .2.2-1+b1 OK!
Raspbian 10 Buster 4.1.6-1~deb10u1+rpt1 OK!
Ubuntu 16.04.3 LTS .8.11-0ubuntu0.16.04.1 OK!
Ubuntu 17.10 3.3.4-2 OK!
Ubuntu 20.04 4.2.2-1ubuntu1 OK!
Suse 42 3.3.4 See notes below not OK
Red Hat 7 FFmpeg must be compiled from sources OK!
Funtoo 7.3.1 3.4.1 FFmpeg needs to be installed with correct "USE flags", see install OK!

Suse does not provide proprietary formats like AAC and H264, thus the distribution FFmpeg is crippled. FFmpegfs will not be able to encode to H264 and AAC. End of story. See

*Tips on other OSs and distributions like Mac or other nixes are welcome.


Mount your filesystem like this:

ffmpegfs [--audiobitrate bitrate] [--videobitrate bitrate] musicdir mountpoint [-o fuse_options]

For example, to run FFmpegfs as daemon, encode to MPEG-4:

ffmpegfs --audiobitrate=256K --videobitrate=1.5M /mnt/music /mnt/ffmpegfs -o allow_other,ro,desttype=mp4

This will run ffmpegs in the foreground and print the log output to the screen:

ffmpegfs -f --log_stderr --audiobitrate=256K --videobitrate=1.5M --audiobitrate=256K --videobitrate=1.5M /mnt/music /mnt/ffmpegfs -o allow_other,ro,desttype=mp4

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

ffmpegfs#/mnt/music /mnt/ffmpegfs fuse allow_other,ro,audiobitrate=256K,videobitrate=2000000,desttype=mp4 0 0

Another (more modern) form of this command:

/mnt/music /mnt/ffmpegfs fuse.ffmpegfs allow_other,ro,audiobitrate=256K,videobitrate=2000000,desttype=mp4 0 0

At this point files like /mnt/music/**.flac and /mnt/music/**.ogg will show up as /mnt/ffmpegfs/**.mp4.

Audio bitrates will be reduced to 256 KBit, video to 1.5 MBit. If the source bitrate is less it will not be scaled up but rather left at the lower value.

Note that the "allow_other" option by default can only be used by root. You must either run FFmpegfs as root or better add a "user_allow_other" key to /etc/fuse.conf.

"allow_other" is required to allow any user access to the mount, by default this is only possible for the user who launched FFmpegfs.


 ffmpegfs -f $HOME/test/in $HOME/test/out --log_stderr --log_maxlevel=DEBUG -o allow_other,ro,desttype=mp4,cachepath=$HOME/test/cache

Run FFmpegfs transcoding files from /test/in to /test/out, logging up to a chatty TRACE level to stderr. The cache resides in test/cache. All directories are under the current user's home directory.

 ffmpegfs -f $HOME/test/in $HOME/test/out --log_stderr --log_maxlevel=DEBUG -o allow_other,ro,desttype=mp4,cachepath=$HOME/test/cache,videowidth=640

Same as above, but also limit video with to 640 pixels. Larger videos will be scaled down, preserving the aspect ratio. Smaller videos will not be scaled up.

 ffmpegfs -f $HOME/test/in $HOME/test/out --log_stderr --log_maxlevel=DEBUG -o allow_other,ro,desttype=mp4,cachepath=$HOME/test/cache,deinterlace

Enable deinterlacing to enhance image quality.

HTTP Live Streaming

ffmpegfs now supports HLS (HTTP Live Streaming). ffmpegfs will create transport stream (ts) segments and the required m3u8 playlists. For your convenience it will also create a virtual test.html file that can playback the segments using the hls.js library (see

To use the new HLS feature invoke ffmpegfs with:

 ffmpegfs -f $HOME/test/in $HOME/test/out -o allow_other,ro,desttype=hls

Please note that this will only work over http, so you need to publish the directory on a web server. Simply navigate to the directory and open test.html. Security restrictions prevent direct playback from disk.


  • Currently the segments are not properly created. Each segment may contain video or audio frames that actually belong to the previous or next segment. This will be fixed in future versions. hls.js does not seem to care about improperly cut segments, though, and playback appears fine. Playing a single segment separately may not work properly.


"Auto copy" performs intelligent stream copy, e.g., if transcoding a transport stream that already represents a H264 video and/or AAC audio stream it would be possible to simply repackage it to a mp4 container without recoding.

This is very efficient as it does not require much computing as de- and encoding does, and it also will not degrade quality as the original file basically stays the same.

The function detects if the target format supports the source codec and simply remuxes the stream even if recoding from one format (e.g. TS) to another (e.g. MOV, MP4).

There are three options:

Option Description
OFF no auto copy
LIMIT only auto copy if target file will not become significantly larger
ALWAY auto copy whenever possible even if the target file becomes larger


Smart transcoding can create different output formats for video and audio files. For example, video files can be converted to ProRes and audio files to AIFF. Of course, combinations like MP4/MP3 or WebM/WAV are possible but do not make sense as MP4 or WebM work perfectly with audio only content.

To use the new feature, simply specify a video and audio file type, separated by a "+" sign. For example, --desttype=mov+aiff will convert video files to Apple Quicktime MOV and audio only files to AIFF. This can be handy if the results are consumed e.g. by some Apple Editing software which is very picky about the input format.


To transcode a video to frame images, set the destination type to JPG, PNG or BMP. This will convert videos to virtual folders with images for each frame.

$ ls /storage/videos

$ ffmpegfs /storage/videos /mnt/ffmpegfs
$ find /mnt/ffmpegfs



Apple's Prores is a so-called intermediate format, intended for post-production editing. It combines highest possible quality while still saving some disk space and not requiring high performance disk systems. On the other hand this means that Prores encoded videos will become quite large - e.g. a 60 minute video may require up to 25 GB.

It is not for target audience use, and certainly not suitable for internet streaming.

Also please keep in mind that when using lossy source formats the quality will not get better, but the files can be fed into software like Final Cut Pro which only accepts a small number of input formats.


The MP4 container has several derivative formats that are not compatible with all target audiences. To feed the resulting files into for example MS Edge, the subformat must be different as for Firefox, unfortunately.

The --profile option allows to select the format:

Profile OS Target Remarks
NONE all VLC, Windows Media Player etc. Playback (default)
FF Linux, Win10, Android Firefox OK: Playback while transcoding
Win7 Firefox OK: Playback while transcoding
EDGE Win10 MS Edge, IE > 11 OK: Playback while transcoding
Win10 Mobile OK: Playback while transcoding
IE Win10 MS IE <= 11 OK: Playback while transcoding
Win7 Must decode first (1)
CHROME all Google Chrome Must decode first (1)
SAFARI Win Apple Safari Must decode first (1)
OPERA All Opera Must decode first (1)
MAXTHON Win Maxthon Must decode first (1)


  • error message when opened while transcoding
  • must start again when file was transcoded
  • Plays fine when file comes directly from buffer

This all boils down to the fact than Firefox and Edge are the only browsers that support the necessary extensions to start playback while still transcoding.

In most cases files will not play if not properly optimised.

See TODO for details.


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 approximately. This works well for MP3 output files, but only fair to good for MP4.

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. Once decoded the file is kept in a disk buffer and can be accessed very fast.

Transcoding is done in an extra thread, so if other processes should access the same file they will share the same transcoded data, saving CPU time. If all processes close the file before its end, transconding will continue for some time. If the file is accessed again before timeout, transcoding will go on, if not it stops and the chunk created so far discarded to save disk space.

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 (but if this is feasible is yet unclear due to restrictions to positioning inside compressed streams).

MP3: ID3 version 2.4 and 1.1 tags are created from the comments in the source file. They are located at the start and end of the file respectively.

MP4: Same applies to meta atoms in MP4 containers.

MP3 target only: 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.

WAV: A pro forma WAV header will be created with estimates of the WAV file size. This header will be replaced when the file is finished. It does not seem necessary, though, as most modern players obviously ignore this information and play the file anyway.


A few words to the supported output formats. There is not much to say about the MP3 output as these are regular MP3 files with no strings attached. They should play well in any modern player.

The MP4 files created are special, though, as MP4 is not quite suited for live streaming. Reason being that the start block of an MP4 contains a field with the size of the compressed data section. Suffice to say that this field cannot be filled in until the size is known, which means compression must be completed first, a file seek done to the beginning, and the size atom updated.

Alas, for a continous live stream, that size will never be known or for our transcoded files one would have to wait for the whole file to be recoded. If that was not enough some important pieces of information are located at the end of the file, including meta tags with artist, album, etc.

Subsequently many applications will go to the end of an MP4 to read important information before going back to the head of the file and start playing. This will break the whole transcode-on-demand idea of FFmpegfs.

To get around the restriction several extensions have been developed, one of which is called "faststart" that relocates the afformentioned data from the end to the beginning of the MP4. Additonally, the size field can be left empty (0). isml (smooth live streaming) is another extension.

For direct to stream transcoding several new features in MP4 need to be active (ISMV, faststart, separate_moof/empty_moov to name them) which are not implemented in older versions of FFMpeg (or if available, not working properly).

By default faststart files will be created with an empty size field so that the file can be started to be written out at once instead of encoding it as a whole before this is possible. Encoding it completely would mean it would take some time before playback can start.

The data part is divided into chunks of about 1 second length, each with its own header, thus it is possible to fill in the size fields early enough.

As a draw back not all players support the format, or play it with strange side effects. VLC plays the file, but updates the time display every few seconds only. When streamed over HTML5 video tags, sometimes there will be no total time shown, but that is OK, as long as the file plays. Playback cannot be positioned past the current playback position, only backwards.

But that's the price of starting playback fast.


Transcoding too slow

See Build FFmpeg with optimisations

Lock ups when accessing through Samba

When accessed via Samba the pending read can lock the whole share, causing Windows Explorer and even KDE Dolphin to freeze. Any access from the same machine to that share is blocked, Even "ls" is not possible and blocks until the data was returned.

Seems others had the same problem:

Adding this to the [global] config in smb.conf fixes that:

oplocks = no
level2 oplocks = no
aio read size = 1

The "aio read size" parameter may be moved to the share config:

aio read size = 1

rsync, Beyond Compare and other tools

Some copy tools do not go along very well with dynamically generated files as in Issue #23: Partial transcode of some files.

Under Linux ist is best to use (optionally with -r parameter)

    cp -uv /path/to/source /path/to/target

This will copy all missing/changed files without missing parts. On the Windows side, Windows Explorer or copy/xcopy work. Tools like Beyond Compare may only copy the predicted size first and not respond to size changes.

Play HLS output by opening hls.html from disk

Most browser prevent playback of files from disk. You may put them into a website directory, but sometimes even https must be used or playback will be blocked.

To enable disk playback in Firefox:

  • Open about:config
  • Set security.fileuri.strict_origin_policy to false


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

git clone

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

FFmpeg library:

Please note that FFmpegfs is in active development, so the main branch may be unstable (but offer nice gimmicks, though). If you need a stable version please get one (preferrably the latest) release.

Feel free to clone this project and add your own features. If they are interesting for others they might be pushed back into this project. Same applies to bug fixes, if you discover a bug your welcome to fix it!

Future Plans

  • Create a windows version
  • and more, see TODO


HLS player and demo code see:


This fork with FFmpeg support is maintained by Norbert Schlia ( since 2017 to date.

Based on work by K. Henriksson (from 2008 to 2017) and the original author David Collett (from 2006 to 2008).

Much thanks to them for the original work and giving me a good head start!


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 and other documentation may be distributed under the GNU Free Documentation License (GFDL) 1.3 or later with no invariant sections, or alternatively under the GNU General Public License (GPL) version 3 or later. The GFDL can be found online or in the COPYING.DOC file.


FFmpeg is licensed under the GNU Lesser General Public License (LGPL) version 2.1 or later. However, FFmpeg incorporates several optional parts and optimizations that are covered by the GNU General Public License (GPL) version 2 or later. If those parts get used the GPL applies to all of FFmpeg.

See for details.


This fork with FFmpeg support copyright (C) 2017-2020 Norbert Schlia (

Based on work Copyright (C) 2006-2008 David Collett, 2008-2013 K. Henriksson.

This is free software: you are free to change and redistribute it under the terms of the GNU General Public License (GPL) version 3 or later.


FUSE-based transcoding filesystem with video support from many formats to MP4, WebM, OGG, MP3, OPUS, MOV, ProRes or WAV.





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