CDI files were originally designed to fit 1GB Dreamcast games onto standard 700MB CD-Rs.
To achieve this "high compression," creators often down-sample audio, reduce movie bitrates, or remove "dummy data".
This format is natively supported by top-tier emulators like Flycast and Redream .
The Sega Dreamcast remains a technological marvel, celebrated for its ahead-of-its-time features like native 480p VGA output and its unique VQ (Vector Quantization) texture compression. For modern enthusiasts, managing a library of these games requires understanding specialized formats to save space without sacrificing the experience.
For most emulation needs, is the premier "highly compressed" format. Developed for the MAME project, it provides lossless compression, meaning no game data, audio, or video quality is lost during the process.
CDI is the essential format if you intend to burn games to disc for use on original hardware (Rev 0 or 1 consoles). Comparison of Compression Formats Compression Type Best Use Case GDI None (Raw) Archive-quality 1:1 rips; GDEMU CHD Lossless Zlib/LZMA General Emulation (Flycast, Redream) Yes CDI Lossy (Asset stripping) Burning to physical CD-Rs Optimizing Your Library
5+ Comprehensive Guides to Burning Dreamcast ROMs onto CD-Rs
To get the most out of your "highly compressed" library, follow these steps: