Flexible Concatenated Archive (FCA)

A flexible container format for embedding multiple files within a single archive file. The FCA format supports version-specific header formats, allowing for extensibility and future enhancements.

Purpose

The Flexible Concatenated Archive (FCA) format is designed to efficiently store and organize multiple embedded files within a single archive. It is optimized for use on extremely low-resource devices, making it ideal for embedded systems, IoT devices, and other constrained environments where memory and processing power are limited.

The format is particularly well-suited for storing collections of related files such as:

• Amiibo dumps (v2 and v3 formats)
• Skylander dumps
• Destiny Infinity dumps
• Lego Dimensions dumps
• Other binary file collections

Design Goals

The FCA format was designed with the following principles in mind:

• Simple - The format is straightforward and easy to understand, with a clear structure that can be implemented with minimal code complexity.

• Efficient - The format wastes as little space as possible, avoiding unnecessary padding or overhead. Every byte serves a purpose.

• Flexible - The format allows room for growth and future expansion through versioning and dynamic header sizes. Different file types can be stored with type-specific metadata.

• Identifiable - The format uses a dedicated file extension (.fca) and magic bytes ("FCA") at the beginning of each file for easy identification.

Overview

FCA files (.fca extension) consist of:

• A global header with magic bytes "FCA" and a version number
• One or more embedded files, each with version-dependent headers containing file type and metadata

See SPEC.md for the complete format specification.

Build self-contained Windows executables

You can package both Python tools as standalone .exe files using PyInstaller.

Prerequisites

• Windows with Python installed
• build dependencies installed in your Python environment

Install build dependencies:

python -m pip install -r python/requirements-build.txt

One-time icon generation

Generate python/small-logo.ico once from python/small-logo.png:

make build-icon

After this, all exe builds reuse python/small-logo.ico directly (no reconversion per build).

Build both executables

From the repository root:

make PYTHON=python build-exes

This generates:

• dist/windows/fca-encode.exe
• dist/windows/fca-decode.exe
• dist/windows/fca-tool.exe

Build individually

make build-exe-encode
make build-exe-decode
make build-exe-tool

If you want to build newer versions of fca-tool.exe, build to a unique filename instead:

make build-exe-tool-unique

This creates dist/windows/fca-tool-<timestamp>.exe and avoids overwriting files.

Clean build artifacts

make clean-build

Unified CLI + GUI tool

Use python/fca_tool.py to run encoding and decoding from a single script.

CLI mode

Encode from an explicit list of files:

python python/fca_tool.py encode --output-file out.fca --input-files file1.bin file2.bin

Encode recursively from one or more directories:

python python/fca_tool.py encode --output-file out.fca --input-dirs dumps/ more_dumps/

You can also combine both:

python python/fca_tool.py encode --output-file out.fca --input-files file1.bin --input-dirs dumps/

Decode an archive:

python python/fca_tool.py decode --input-file out.fca --output-dir extracted

GUI mode

Launch GUI directly:

python python/fca_tool.py --gui

If run without subcommands, GUI mode starts automatically. In the GUI Encode tab, you can add individual files or add a folder recursively.

GitHub Actions build

This repository includes a workflow at .github/workflows/build-exes.yml that builds:

• fca-encode.exe
• fca-decode.exe
• fca-tool.exe

Targets:

• windows-x64 on GitHub-hosted windows-latest
• windows-arm64 on a self-hosted runner labeled self-hosted, Windows, ARM64 (manual workflow dispatch only)

The workflow runs windows-x64 on push, pull_request, and workflow_dispatch. The windows-arm64 job runs only when manually triggered with build_arm64=true.