NAME¶

ffmpegfs - mounts and transcodes a multitude of formats to one of the target formats on the fly.

SYNOPSIS¶

ffmpegfs [OPTION]... IN_DIR OUT_DIR

DESCRIPTION¶

The ffmpegfs(1) command will mount the directory IN_DIR on OUT_DIR. Thereafter, accessing OUT_DIR will show the contents of IN_DIR, with all supported media files transparently renamed and transcoded to one of the supported target formats upon access.

Supported output formats:

OPTIONS¶

Usage: ffmpegfs [OPTION]... IN_DIR OUT_DIR

Mount IN_DIR on OUT_DIR, converting audio and video files upon access.

USAGE¶

Mount your file system as follows:

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

To use FFmpegfs as a daemon and encode to MPEG-4, for instance:

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

This will run FFmpegfs 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

With the following entry in "/etc/fstab," the same result can be obtained with more recent versions of FUSE:

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

Another (more current) way to express 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. The source bitrate will not be scaled up if it is lower; it will remain at the lower value.

Keep in mind that only root can, by default, utilise the "allow other" option. Either use the "user allow other" key in /etc/fuse.conf or run FFmpegfs as root.

Any user must have "allow other" enabled in order to access the mount. By default, only the user who initiated FFmpegfs has access to this.

Examples:

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

Transcode files using FFmpegfs from test/in to test/out while logging to stderr at a noisy TRACE level. 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

Similar to the previous, but with a 640-pixel maximum video width. The aspect ratio will be maintained when scaling down larger videos. Videos that are smaller won’t 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

Deinterlacing can be enabled for better image quality.

HOW IT WORKS¶

The decoder and encoder are initialised when a file is opened, and the file’s metadata is also read. At this point, a rough estimate of the total file size can be made. Because the actual size greatly depends on the material encoded, this technique works fair-to-good for MP4 or WebM output files but works well for MP3, AIFF, or WAV output files.

The file is transcoded as it is being read and stored in a private per-file buffer. This buffer keeps expanding as the file is read until the entire file has been transcoded. After being decoded, the file is stored in a disc buffer and is readily accessible.

Other processes will share the same transcoded data if they access the same file because transcoding is done in a single additional thread, which saves CPU time. Transcoding will continue for a while if all processes close the file before it is finished. Transcoding will resume if the file is viewed once more before the timer expires. If not, it will halt and delete the current chunk to free up storage space.

A file will be transcoded up to the seek point when you seek within it (if not already done). Since the majority of programmes will read a file from beginning to end, this is typically not a problem. Future upgrades might offer actual random seeking (but if this is feasible, it is not yet clear due to restrictions to positioning inside compressed streams). When HLS streaming is chosen, this already functions. The requested segment is immediately skipped to by FFmpegfs.

MP3: The source file’s comments are used to generate ID3 version 2.4 and 1.1 tags. They are correspondingly at the beginning and the end of the file.

MP4: The same is true for meta atoms contained in MP4 containers.

WAV: The estimated size of the WAV file will be included in a pro forma WAV header. When the file is complete, this header will be changed. Though most current gamers apparently disregard this information and continue to play the file, it does not seem required.

Only for MP3 targets: A particular optimization has been done so that programmes that look for id3v1 tags don’t have to wait for the entire file to be transcoded before reading the tag. This accelerates these apps dramatically.

ABOUT OUTPUT FORMATS¶

A few remarks regarding the output formats that are supported:

Since these are plain vanilla constant bitrate (CBR) MP3 files, there isn’t much to say about the MP3 output. Any modern player should be able to play them well.

However, MP4 files are unique because standard MP4s aren’t really ideal for live broadcasting. The start block of an MP4 has a field with the size of the compressed data section, which is the cause. It suffices to say that until the size is known, compression must be finished, a file seek must be performed to the beginning, and the size atom updated.

That size is unknown for a live stream that is ongoing. To obtain that value for our transcoded files, one would need to wait for the entire file to be recoded. As if that weren’t enough, the file’s final section contains some crucial details, such as meta tags for the artist, album, etc. Additionally, the fact that there is just one enormous data block makes it difficult to do random searches among the contents without access to the entire data section.

Many programmes will then read the crucial information from the end of an MP4 before returning to the file’s head and beginning playback. This will destroy FFmpegfs' entire transcode-on-demand concept.

Several extensions have been created to work around the restriction, including "faststart," which moves the aforementioned meta data from the end to the beginning of the MP4 file. Additionally, it is possible to omit the size field (0). An further plugin is isml (smooth live streaming).

Older versions of FFmpeg do not support several new MP4 features that are required for direct-to-stream transcoding, like ISMV, faststart, separate moof/empty moov, to mention a few (or if available, not working properly).

Faststart files are produced by default with an empty size field so that the file can be started to be written out at once rather than having to be encoded as a complete first. It would take some time before playback could begin if it were fully encoded. The data part is divided into chunks of about 1 second each, all with their own header, so it is possible to fill in the size fields early enough.

One disadvantage is that not all players agree with the format, or they play it with odd side effects. VLC only refreshes the time display every several seconds while playing the file. There may not always be a complete duration displayed while streaming using HTML5 video tags, but that is fine as long as the content plays. Playback can only move backwards from the current playback position.

However, that is the cost of commencing playback quickly.

DEVELOPMENT¶

Git is the revision control system used by FFmpegfs. The complete repository is available here:

git clone https://github.com/nschlia/ffmpegfs.git

or the mirror:

git clone https://salsa.debian.org/nschlia/ffmpegfs.git

FFmpegfs is composed primarily of C++17 with a small amount of C. The following libraries are utilised:

FFmpeg home pages:

FILES¶

/usr/local/bin/ffmpegfs, /etc/fstab

AUTHORS¶

This fork with FFmpeg support has been 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!

LICENSE¶

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.

FFMPEG LICENSE¶

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 https://www.ffmpeg.org/legal.html for details.

COPYRIGHT¶

This fork with FFmpeg support copyright (C) 2017-2023 Norbert Schlia.

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

Much thanks to them for the original work!

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.

This manual is copyright (C) 2010-2011 K. Henriksson and (C) 2017-2023 by N. Schlia and 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.