AosTools
Commandline toolset for extracting/repacking .aos archives and decoding/encoding it's associated files.
Start to release year: 2023 - 2025
Programming language: C# (.NET)
Project
AosTools is a commandline tool for extracting and repacking .aos archives used by various visual novel producers with their in-house engine. This tool makes modding and translation of the game files possible.
I started this project as passion project and to challenge my own limits. Most of the project consisted of research, reverse engineering and trial & error.
Biggest challenges during the project were figuring out what kind of format the game files are stored in and how to decode them into a common readable format.
This required me to figure out if the files are encrypted and/or compressed and what kind of methods they used to do that. What made this difficult was the lack of information about the game engine which made analyzing the files and executables extremely important. This made sense since the engine was built for internal use only and was never meant to be used by outsiders.
I also had to analyze how the engine itself behaved, so I got good amount of hours into assembly since the engine was compiled from C++ to machine code.
Key features
- Reading and writing .aos archive files
- Script file compression and decompression using huffman coding algorithm
- Bitmap unpacking using run-length encoding (RLE)
- Custom bitmap animation format extraction
Formats the tool is able to extract or decode:
| Format | Description |
|---|---|
| .aos | Archive format used for storing files. |
| .scr | Huffman compressed text file used for storing scripts. |
| .bmp | Bitmap graphic. |
| .abm | Custom bitmap format that can be compressed or store multi frame animations. |
| .msk | Grayscale bitmap mask used for transitions and similar effects. |
| .ogg | Sound file. |
Repository
The project source and release build are available on my GitHub.