CSOChef

Python-based ISO <-> CSO compressor and decompressor for PSP images.
It allows compressing PlayStation Portable (PSP) ISO files to CSO format with configurable compression level and alignment, and decompressing CSO back to ISO.
Can be used even by users without Python installed (can be compiled into an executable).

Works on Windows, Linux, and MacOS.

Features

• Compress ISO → CSO
• Decompress CSO → ISO
• Optional SHA-1 verification to ensure CSO integrity (--verify)
• Multithreading support for faster decompression (-mt)
• Adjustable compression level (-l 0-9)
• Adjustable alignment for CSO padding (-a 0-6)
• Progress bar during compression/decompression
• Works with most standard CSOs (alignment 0–3 fully supported)
• Temporary verification ISO automatically cleaned up

Requirements

• Python 3.10+ (Optional, only if you're running csochef.py)
• zlib (standard Python module, only if running csochef.py)

Installation

Option 1: Use the Windows executable (recommended)

1. Go to the Releases page.
2. Download csochef.exe.
3. Place it in a folder with your ISO or CSO file.
4. Run from Command Prompt:

csochef.exe compress demo.iso demo.cso
csochef.exe decompress demo.cso demo_decompressed.iso

Option 2: Run from Python

1. Make sure Python 3.10 (or higher) is installed.
2. Clone this repository:

git clone https://github.com/RetroChef/csochef.git
cd csochef

Start compressing/decompressing:

Compress ISO to CSO

python csochef.py compress demo.iso demo.cso

Decompress CSO to ISO

python csochef.py decompress demo.cso demo_decompressed.iso

Usage

python csochef.py <mode> <input> <output> [options]

Arguments

mode - Choose compress to create a CSO, or decompress to extract an ISO
input - Input file path (ISO for compress, CSO for decompress)
ouput - Output file path (CSO for compress, ISO for decompress)

Options

-l, --level            Compression level 0–9. 0 = fast/larger, 9 = small/slower
-a, --align            Padding alignment 0–6. Higher numbers = faster but may break some decompressors
--verify               Verify CSO by decompressing and comparing SHA1 hash with original ISO
-mt, --multithread     Enable multithreaded decompression for faster performance

Examples

Compress ISO to CSO with default settings:

csochef.exe compress demo.iso demo.cso

Compress ISO with alignment 2 and compression level 5

csochef.exe compress demo.iso demo.cso -a 2 -l 5

Compress ISO and verify CSO integrity

csochef.exe compress demo.iso demo.cso --verify

Decompress CSO to ISO:

csochef.exe decompress demo.cso demo_decompressed.iso

Decompress CSO to ISO using multithreading for faster extraction:

csochef.exe decompress demo.cso demo_decompressed.iso -mt

Compress ISO with all options (alignment, level, verify)

csochef.exe compress demo.iso demo.cso -a 1 -l 7 --verify

Notes

Multithreading only applies to decompression, not compression.

CSOs with alignment 4–6 may fail to decompress in some tools, including CSOChef.

Verification will temporarily create a file named verify_temp.iso during hash comparison and remove it afterward.