renpak

AVIF compression toolchain for Ren'Py games. Shrinks RPA archives by re-encoding images to AVIF — games load them transparently at runtime, no engine patches needed.

https://github.com/user-attachments/assets/46800098-0db3-4de7-a442-b2dbd0fb5fb1

Why bother

Ren'Py visual novels ship massive RPA archives full of WebP and PNG images. AVIF, built on the AV1 video codec, compresses them 3–5x smaller at comparable visual quality.

renpak handles the whole pipeline: crack open the RPA, re-encode every image in parallel, write a new archive with an embedded manifest, and drop in a tiny runtime plugin that hooks Ren'Py's file loading. The game never knows the difference.

Results

Tested on Eternum v0.9.5 (latest public release), Medium preset (quality 60, speed 8):

| | Original | Compressed | | |---|---|---|---| | RPA archive | 11.3 GiB | 7.2 GiB | 1.56x smaller | | Image data | 5.11 GiB | 1.08 GiB | 4.73x smaller |

12,732 images (12,243 JPG + 379 WebP + 110 PNG → AVIF) in 9 min 28 sec on an i7-12650H.

| Metric | Mean | Median | Range | | |--------|------|--------|-------|-| | SSIM ↑ | 0.950 | 0.957 | 0.892 – 1.000 | 1.0 = identical, >0.95 visually indistinguishable | | LPIPS ↓ | 0.071 | 0.065 | 0.000 – 0.180 | 0.0 = identical, <0.1 near-transparent to human eyes |

Install

# Linux / macOS
curl -fsSL https://renpak.vercel.app/install | bash

# Windows (PowerShell)
irm https://renpak.vercel.app/install.ps1 | iex

Downloads a static binary to ~/.local/bin (Unix) or %USERPROFILE%\.local\bin (Windows).

Build from source

Needs a Rust toolchain and system libavif:

# Arch
sudo pacman -S libavif

# Ubuntu / Debian
sudo apt install libavif-dev

# macOS
brew install libavif

git clone https://github.com/NihilDigit/renpak.git
cd renpak
cargo build --release
./install.sh  # symlinks to ~/.local/bin/renpak

Quickstart

Open a terminal in the game directory and run:

renpak

1. Select which RPA archives to compress
2. Pick a quality preset (Medium is a good default)
3. Hit Start — renpak encodes all images in parallel

When encoding finishes, hit Install. The original RPA is backed up to .renpak_backup/, and the compressed archive takes its place. You'll then see:

• Launch — start the game to verify everything looks right
• Revert — restore the original RPA from backup
• Delete — remove the backup to free disk space (only do this after you've verified the game)
• Quit — exit renpak

Usage

cd into a game directory and run renpak with no arguments, or pass a path explicitly.

Quality presets:

| Preset | Quality | Speed | Use case | |--------|---------|-------|----------| | High | 75 | 6 | Archival, picky about artifacts | | Medium | 60 | 8 | Default — good balance | | Low | 40 | 10 | Maximum compression, fast |

Headless mode

renpak build input.rpa output.rpa [options]

| Flag | Description | |------|-------------| | -p, --preset | high, medium, or low | | -q, --quality | AVIF quality 0–100 (overrides preset) | | -s, --speed | Encoder speed 0–10 (overrides preset) | | -w, --workers | Thread count (default: all cores) | | -x, --exclude | Skip files matching prefix (repeatable) |

How it works

Build phase. Reads the RPA-3.0 index, decodes each image to RGBA, encodes to AVIF via libaom (YUV444, full range, BT.709 color). Writes a new RPA with renamed entries and a JSON manifest. Encoding is parallelized with Rayon; already-encoded frames are cached to disk so re-runs skip them.

Runtime phase. Two files go into game/:

• renpak_init.rpy — bootstraps at init -999, before any game code
• renpak_loader.py — hooks file_open_callback (name remapping), loadable_callback (keeps declarations working), and monkey-patches load_image (fixes SDL2_image extension hint for AVIF)

No engine modifications. Standard Ren'Py extension points only.

Project layout

crates/renpak-core/     Build engine: RPA I/O, AVIF encoding, TUI, CLI
crates/renpak-rt/       Runtime decoder: AVIS frame-level random access (C ABI)
python/runtime/         Ren'Py plugin (deployed to game/)
web/                    Install scripts (Vercel-hosted)

License

MPL-2.0