fcx 0.1.3

File conversion exchange for Linux: one command routes files to pandoc, ImageMagick, LibreOffice & more through an extensible converter registry.

fcx — File Conversion Exchange

fcx is a file conversion exchange for Linux — one command routes your files to the right backend (pandoc, ImageMagick, LibreOffice, Inkscape…) through an extensible converter registry.

Motivation

Linux power users who regularly convert files face a fragmented landscape: pandoc for documents, convert for images, loffice --headless for Office files, pdftotext for PDF extraction, ffmpeg for audio. Each tool has a different interface, different flag conventions, and different merging semantics. Scripting across them requires memorising or looking up the invocation for every combination.

fcx provides a single, consistent command for all of these:

fcx report.pdf intro.pdf chapter.docx diagram.svg   # merge to pdf
fcx jpg:l2 photos/*.jpg                             # batch compress
fcx wav:16k recordings/*.mp3                        # audio normalisation

The tool is especially useful in Makefiles, shell scripts, and AI coding agent pipelines where you want one deterministic command to handle whatever input format you have.

Installation

pip3 install fcx

# or in an isolated environment
pipx install fcx

# upgrade
pip3 install --upgrade fcx

From source

git clone https://github.com/sjjsy/fcx.git
cd fcx
pip3 install -e .

Quick start

fcx chapter.md appendix.md          # → chapter.pdf (merge via pandoc)
fcx txt notes.md paper.pdf          # → notes.txt  (merge, pandoc + pdftotext)
fcx png *.svg                       # → per-file PNG (inkscape or ImageMagick)
fcx jpg:l1 photos/*.jpg             # compress in-place, backup to Trash
fcx jpg:crop:50x50 *.jpg            # center-crop 50% each axis, backup to Trash
fcx wav:16k recordings/*.mp3        # → per-file 16 kHz mono WAV
fcx -R                              # recover last in-place backup from Trash

System requirements

fcx itself requires only Python 3.8+ and docopt. Converters require their respective backend tools:

Tool	Purpose	Install
pandoc	md/rst/html/docx → pdf/txt/md/rst/html	apt install pandoc
ImageMagick	image ↔ image, →pdf, in-place transforms	apt install imagemagick
LibreOffice	docx/pptx/xlsx/odt → pdf/txt	apt install libreoffice
wkhtmltopdf	html → pdf (also used by pandoc)	apt install wkhtmltopdf
Inkscape	svg → pdf/png	apt install inkscape
pdflatex	tex/tikz → pdf	apt install texlive-latex-base
poppler-utils	pdf → txt (pdftotext), pdf merge (pdfjam)	apt install poppler-utils
ffmpeg	audio/video → wav	apt install ffmpeg
jpegoptim	JPG lossy compression	apt install jpegoptim
jpegtran	JPG lossless optimisation	apt install libjpeg-turbo-progs
optipng	PNG optimisation	apt install optipng

Only the tools needed for your conversions need to be installed. Use fcx -d to check what is available.

CLI reference

fcx — File Converter

Convert files to a different format or apply in-place transforms.
Inputs are merged (pdf, txt) or converted individually (img, same-format).

Usage:
  fcx [options] [ARGS ...]
  fcx -h | --help
  fcx --version

Options:
  -h --help        Show this screen.
  --version        Show version.
  -I --init        Copy built-in converter file(s) to ~/.config/fcx/converters/.
  -d --deps        Check deps for all converters, or for named TARGET ext(s).
  -m --methods     List all converters for each TARGET ext.
  -i --inputs      List input extensions that can produce each output ext.
  -o --outputs     List output extensions producible from each input ext.
  -R --recover     Restore most-recent fcx backup from Trash into CWD.
  -O --overwrite   Skip trash backup for same-format (in-place) transforms.
  -v --verbose     Stream live stdout/stderr from every shell command.
  --dry-run        Print commands without executing.

TARGET syntax:
  The first positional argument is treated as TARGET when it does not name an
  existing file on disk.  It takes the form  SPEC[:METHOD[:PARAMS]]  where:

    SPEC     Output extension (pdf, txt, png, jpg, wav, ...) or explicit output
             file path (report.pdf, out/notes.txt, ...).
             Omit entirely to default to "pdf".
    METHOD   Name or unique prefix of the converter to prefer, e.g.
             pandoc, loffice, wk, l1, crop.  Fuzzy prefix-matched against
             converter names; falls back to the next available converter.
    PARAMS   Parameter string passed verbatim to the converter function.
             Some converters require it (e.g. crop:50x50, annotate:Draft v2).

  Examples:
    pdf                  pdf:pandoc            jpg:l1
    jpg:crop:50x50       jpg:annotate:Draft v2 report.pdf:loffice
    wav:16k

Output file naming:
  SPEC is a path  → that is the output file.
  SPEC is an ext, merge mode (→pdf/txt)  → {first_input_stem}.{ext} in CWD.
  SPEC is an ext, per-file mode          → {each_input_stem}.{ext} in CWD.
  Same-format transform                  → input file path (in-place).

Trash backup (same-format transforms):
  Before in-place transforms, inputs are copied to:
    ~/.local/share/Trash/files/fcx_YYYYMMDD_HHMMSS_EXT/
  with a matching .trashinfo sidecar.  No external tools needed.
  Use -R / --recover to restore the most recent backup into CWD.
  Use -O / --overwrite to skip the backup entirely.

Examples:
  fcx report.pdf intro.pdf chapter.docx diagram.svg   # merge → pdf
  fcx pdf report.pdf intro.pdf chapter.docx           # same, explicit ext
  fcx txt notes.txt paper.pdf slides.pptx             # merge → txt
  fcx png *.svg                                       # batch svg → png
  fcx report.pdf:pandoc chapter.md appendix.md        # force pandoc
  fcx jpg:l1 photos/*.jpg                             # compress to trash
  fcx jpg:l1 -O photos/*.jpg                          # compress, no backup
  fcx jpg:crop:50x50 photos/*.jpg                     # center-crop 50%
  fcx jpg:annotate:Draft v2 *.jpg                     # annotate all
  fcx wav:16k recordings/*.mp3                        # audio → 16 kHz mono
  fcx -R                                              # recover last backup
  fcx -R jpg                                          # recover last jpg backup
  fcx -d                                              # check all deps
  fcx -d pdf                                          # check →pdf converter deps
  fcx -m pdf                                          # list all →pdf converters
  fcx -o docx                                         # what can docx become?
  fcx -i pdf                                          # what converts to pdf?
  fcx -I                                              # list built-in converter files
  fcx -I pandoc                                       # copy pandoc.py to user config dir

Registered converters

→ PDF (merge mode)

From formats	Converter	Backend	Notes
pdf	builtin-copy-pdf	—	Passthrough / copy
jpg, png, gif, bmp, tiff, webp	imagemagick	convert	Direct image→PDF
svg	inkscape-pdf	inkscape	High-fidelity vector
svg	imagemagick-svg-pdf	convert	Fallback
docx, odt, pptx, xls, xlsx, rtf, csv	libreoffice	loffice --headless
md, rst, html, xhtml, docx, rtf, txt	pandoc-wk	pandoc + wkhtmltopdf	Best pandoc output
md, rst, html, tex, csv, …	pandoc	pandoc	Fallback
html, xhtml, htm	wkhtmltopdf	wkhtmltopdf
tex, tikz	pdflatex	pdflatex	Auto-runs biber/makeglossaries

→ TXT (merge mode)

From formats	Converter	Backend
txt, md, rst	builtin-copy-txt	—
pdf	pdftotext	pdftotext
any above	builtin-via-pdf	chains →pdf, then pdftotext

→ Markup (merge mode)

To format	Converter	Backend
md	pandoc-md	pandoc
rst	pandoc-rst	pandoc
html	pandoc-html	pandoc

→ Image format conversion (per-file)

From	To	Converter	Backend
svg	pdf	inkscape-pdf	inkscape
svg	png	inkscape-png	inkscape
svg	jpg	inkscape-jpg	inkscape + convert
any image	png	imagemagick-to-img	convert
any image	jpg	imagemagick-to-jpg	convert

→ JPG in-place transforms (per-file, trash backup)

METHOD	Deps	Effect
l0	jpegtran	Lossless optimise + progressive
l1	jpegoptim	q 85
l2	jpegoptim, convert	q 75; resize if > 2666 px
l3	jpegoptim, convert	q 60; resize if > 800 px
luh	convert	Fit 3840×2160, q 90
lum	convert	Fit 3840×2160, q 60
lul	convert	Fit 3840×2160, q 40
lfh	convert	Fit 1920×1080, q 90
lfm	convert	Fit 1920×1080, q 60
lfl	convert	Fit 1920×1080, q 40
lm	convert	Fit 800×800, q 60
lb1	convert	B&W document binarise
crop	convert, identify	Center-crop percentage per axis (PARAMS: WxH)
cropabs	convert, identify	Center-crop in pixels (PARAMS: WxH)
annotate	convert, identify	Overlay text label at bottom (PARAMS: text)
version	convert, jpegtran, jpegoptim	Creates ver/ with l0–l3 comparison set
montage	convert	Square-crop + assemble montage grid (PARAMS: cell_px)

→ PNG in-place transforms

METHOD	Deps	Effect
l0-png	optipng	Lossless optimise
l1-png	optipng	Aggressive lossless optimise
l2-png	optipng, convert	Resize if > 2666 px
l3-png	optipng, convert	Resize if > 800 px
lb1-png	convert	B&W document binarise
crop-png	convert, identify	Center-crop percentage (PARAMS: WxH)
cropabs-png	convert, identify	Center-crop in pixels (PARAMS: WxH)
annotate-png	convert, identify	Overlay text label

→ WAV (per-file)

From formats	Converter	Backend	Effect
mp3, m4a, ogg, flac, aac, opus, wma, wav, mp4, …	ffmpeg-16k	ffmpeg	16 kHz mono WAV

Checking what is available

fcx -d                   # all converters and their deps
fcx -d pdf               # deps for →pdf converters only
fcx -m pdf               # list all →pdf converters, which would be selected
fcx -m jpg               # list all →jpg converters
fcx -i pdf               # what input formats can produce pdf?
fcx -o docx              # what output formats can docx produce?

Extending fcx

Converters live in CONVERTERS lists inside Python files. Three layers are merged at startup — later layers win for same-named converters; unique names coexist with user/system versions listed first:

1. built-in   fcx/converters/*.py         (ships with fcx)
2. system     /etc/xdg/fcx/converters/*.py
3. user       ~/.config/fcx/converters/*.py   ← highest priority

Add a custom converter

Copy a built-in converter file to your user config dir:

fcx -I pandoc              # copies pandoc.py to ~/.config/fcx/converters/pandoc.py
fcx -I                     # list all built-in converter files

Then edit the copy. Delete the file to revert to the built-in.

Write one from scratch

Create ~/.config/fcx/converters/mytools.py:

from pathlib import Path
from typing import List, Optional
from fcx.core import Converter, run

def _my_converter(srcs: List[Path], dst: Path, params: Optional[str]) -> None:
    run(["mytool", "--output", str(dst)] + [str(s) for s in srcs])

CONVERTERS = [
    Converter(
        name="mytool",
        from_formats=("md",),
        to_format="pdf",
        deps=["mytool"],
        params=None,
        fn=_my_converter,
        mode="merge",     # "merge" | "per-file" | "in-place" | "auto"
    ),
]

Verify: fcx -d pdf and fcx -m pdf.

Converter dataclass

@dataclass
class Converter:
    name: str                 # matched by METHOD prefix in TARGET
    from_formats: tuple       # input extensions (lowercase, no dot)
    to_format: str            # output extension
    deps: list                # binary names checked on PATH
    params: str | None        # human-readable PARAMS description, or None
    fn: Callable              # fn(srcs: list[Path], dst: Path, params: str | None)
    mode: str = "auto"        # dispatch mode (see above)

Dispatch mode

mode	behaviour
"auto"	merge if to_format in (pdf, txt); in-place if to==from; else per-file
"merge"	all inputs passed to fn at once, one output
"per-file"	fn called once per input, no trash backup
"in-place"	fn called once per input, trash backup before first call

Verbose and dry-run

fcx -v jpg:l1 photo.jpg     # stream live output from jpegoptim
fcx --dry-run pdf *.md      # print commands without running them

Examples

# Document conversion
fcx report.pdf chapter.md appendix.md      # merge md → pdf
fcx txt notes.pdf slides.pptx              # merge to txt
fcx html document.docx                     # docx → html via pandoc

# Image conversion
fcx png *.svg                              # batch svg → png (inkscape)
fcx jpg diagram.svg                        # svg → jpg

# In-place image compression (all backed up to Trash first)
fcx jpg:l1 photos/*.jpg                    # compress to q85
fcx jpg:l2 photos/*.jpg                    # q75, resize if > 2666px
fcx jpg:l3 -O photos/*.jpg                 # q60, no backup (--overwrite)
fcx jpg:luh portraits/*.jpg                # fit 4K UHD, q90

# In-place image transforms
fcx jpg:crop:75x75 thumbnails/*.jpg        # center-crop to 75%
fcx jpg:cropabs:800x800 pics/*.jpg         # center-crop to 800×800px
fcx jpg:annotate:Draft *.jpg               # overlay label "Draft"
fcx jpg:lb1 scans/*.jpg                    # binarise to B&W document

# PNG optimisation
fcx png:l1-png images/*.png                # aggressive lossless optimise
fcx png:crop-png:80x80 icons/*.png         # center-crop PNGs

# Comparison sets and montage
fcx jpg:version photo.jpg                  # creates ver/ with l0–l3 comparison
fcx jpg:montage *.jpg                      # assemble 300×300 montage grid

# Audio
fcx wav:16k recordings/*.mp3               # 16 kHz mono WAV for ASR
fcx wav:16k interview.m4a                  # single file

# Dependency check
fcx -d                                     # all converters
fcx -d jpg                                 # only jpg-related converters

# Discovery
fcx -m pdf                                 # what converters exist for →pdf?
fcx -i pdf                                 # what can be converted to pdf?
fcx -o docx                                # what can docx become?

# Recovery
fcx -R                                     # restore last backup
fcx -R jpg                                 # restore last jpg backup

Contributing

Fork the repository and open a pull request. Adding converters for new backend tools is the most welcome contribution — each converter file is self-contained and easy to write.

License

GNU Affero General Public License v3.0 — see LICENSE.

---

Related projects

fcx sits at the intersection of document conversion and image processing automation. The tables below place it in context.

Document conversion backends

These are the system tools that fcx dispatches to. Each has a different sweet spot; fcx selects the best available one automatically.

Tool	License	Best for	Used in fcx
pandoc	GPL-2	Universal markup converter; md/rst/html/docx → pdf/html/txt and 50+ formats	Yes — pandoc, pandoc-wk
LibreOffice	MPL-2	Office formats (docx/pptx/xlsx/odt) headless conversion	Yes — libreoffice (via loffice --headless)
wkhtmltopdf	LGPL-3	HTML → PDF with full CSS/JS rendering (WebKit engine)	Yes — wkhtmltopdf
ImageMagick	Apache-2	Image ↔ image, raster → PDF, compositing	Yes — convert, identify, montage
Inkscape	GPL-3	SVG → PDF/PNG with full vector fidelity	Yes — inkscape --export-type
pdflatex / TeX Live	Mixed/Free	TeX → PDF with bibliography and glossary management	Yes — pdflatex, biber, makeglossaries
poppler-utils	GPL-2	PDF text extraction (pdftotext), PDF merge (pdfjam)	Yes — pdftotext, pdfjam
ffmpeg	LGPL-2.1	Audio/video format conversion	Yes — ffmpeg-16k
jpegoptim	GPL-2	Lossy JPG compression with quality targets	Yes — l1–l3 converters
jpegtran	BSD	Lossless JPG transform and optimisation	Yes — l0 converter
optipng	zlib/libpng	Lossless PNG compression	Yes — l0-png–l3-png
Weasyprint	BSD	HTML → PDF via Python (no Qt/WebKit); CSS Paged Media	No — alternative to wkhtmltopdf
unoconv	GPL-2	LibreOffice UNO bridge; similar to loffice --headless	No — superseded by loffice --headless

Python document conversion libraries

Pure Python or wrapper libraries that avoid shelling out. fcx prefers system tools for flexibility but these are useful when you need embedded conversion.

Library	License	Stars	Best for
pypandoc	MIT	1.3k	Python wrapper around pandoc; supports all pandoc formats
docx2pdf	MIT	2.1k	DOCX → PDF on macOS (Word) / Linux (LibreOffice)
img2pdf	LGPL-3	1.0k	Lossless image → PDF; preserves original pixels without re-encoding
pdf2image	MIT	1.8k	PDF → PIL Image objects via poppler
python-pptx	MIT	2.6k	Read/write PPTX; no built-in PDF export
pymupdf	AGPL-3 / commercial	4.8k	High-speed PDF/XPS/EPUB rendering, extraction, annotation
weasyprint	BSD	7.1k	HTML/CSS → PDF in Python; CSS Paged Media support

Batch file conversion tools

CLI and GUI tools that wrap multiple conversion backends — the category closest to fcx itself.

Tool	Type	Platform	License	Formats	Notes
fcx (this)	CLI	Linux	AGPL-3	docs, images, audio	Extensible registry; in-place transforms; trash backup; scriptable
fileConverter	GUI	Windows	GPL-3	images, audio, video, docs	Right-click shell extension; uses ffmpeg/ImageMagick
unoconv	CLI	Linux/macOS	GPL-2	office formats only	LibreOffice UNO bridge; no longer actively maintained
pandoc	CLI	Any	GPL-2	markup/docs only	The gold standard for document conversion; no images or audio
Converseen	GUI	Linux/Windows	GPL-3	images only	Qt/ImageMagick batch image converter
Kramdown-AsciiDoc	CLI	Any	MIT	md → asciidoc	Single format pair, deep conversion fidelity

Image optimisation CLIs

Tools focused on reducing image file size. fcx wraps these under a consistent interface with trash backup.

Tool	License	Algorithm	In fcx
jpegoptim	GPL-2	Progressive JPEG; quality targets; strips metadata	Yes — l1, l2, l3
jpegtran	BSD	Lossless DCT operations; progressive scan	Yes — l0
optipng	zlib	Lossless PNG deflate optimisation	Yes — l0-png–l3-png
pngquant	GPL-3	Lossy PNG palette quantisation (often 60–80% savings)	No — lossy; would fit a future l1-png lossy variant
oxipng	MIT	Multi-threaded lossless PNG (Rust); faster than optipng	No — could replace optipng as a future built-in
Squoosh CLI	Apache-2	WASM-based multi-format image optimisation	No — Node.js dependency
ImageOptim-CLI	MIT	Orchestrates multiple tools (jpegtran, pngquant, …)	No — macOS-native tools