Convert MDF to CDI

Older DiscJuggler software and some Sega Dreamcast emulators or burning workflows require a .cdi image instead of Alcohol 120%’s .mdf/.mds pair. Conversion is needed for that compatibility; changing the filename extension does not change the image format.

What the MDF format is

.mdf is the main data file in an Alcohol 120% disc image. Its companion .mds file stores the disc layout, track and session boundaries, sector information, and other metadata required to interpret the MDF correctly.

MDF/MDS images can contain data CDs, mixed-mode discs, audio tracks, multisession media, and some copy-protected layouts. Keep both files in the same folder and use the .mds file when opening or mounting the image. An MDF without its matching MDS may be impossible to convert accurately.

What the CDI format is

.cdi is the proprietary disc-image format associated with Padus DiscJuggler. Older DiscJuggler burning software uses it, and it is common in archived Sega Dreamcast releases because it can represent boot information, raw sectors, data tracks, and audio tracks in layouts expected by the console.

CDI is not a universal or modern replacement for MDF/MDS. Its advantages are compatibility with DiscJuggler-era software and some Dreamcast tools; its disadvantages are limited current support, opaque structure, and incompatibility between some CDI images and burners or emulators.

How to convert a standard CD image

1. Make a backup of source.mdf and source.mds. Do not work from an MDF that has been separated from its descriptor file.
2. Install a program that can mount MDS/MDF images, such as Alcohol 120% or DAEMON Tools, and mount source.mds in a virtual optical drive.
3. Install Padus DiscJuggler, preferably in an isolated older Windows environment because current operating systems may not support its driver. Use its CD-image creation function, select the mounted optical drive as the source, and choose a destination such as output.cdi.
4. Choose the source and sector options that match the original disc. Raw sectors, multiple sessions, audio tracks, and copy-protection data require more than a simple ISO-style file copy, and a virtual drive may not expose the original subchannel data.
5. Open the resulting CDI in a compatible emulator or image utility and check its track count, track types, file listing, and boot behavior before burning it. Keep the original MDF/MDS pair until those checks succeed.

DiscJuggler may fail to read a virtual drive, and mounting can hide information that was present in the original image. If the image contains only a normal data track, extract the files with IsoBuster and create a new CDI from a physical or virtual disc. This preserves the files but not necessarily the original boot sectors, protection, sessions, pregaps, or subchannel data.

How to handle a Dreamcast image

Do not first convert a Dreamcast MDF/MDS image to a plain ISO. ISO output can discard audio tracks, raw sector modes, session boundaries, and the boot structure required by the console.

1. Open the .mds file in IsoBuster and inspect the sessions and tracks. Extract the tracks as raw binary data where the program supports it, retaining their original order and sector modes.
2. Create or preserve a matching .cue file if the extracted material contains multiple data or audio tracks. Check the cue sheet against the original track layout.
3. Use a Dreamcast-specific CDI authoring tool that explicitly supports the source track modes, such as bin2boot for compatible BIN/CUE input. Follow the utility’s version-specific syntax and verify that it creates the required self-boot or bootable layout.
4. Test the CDI in a Dreamcast emulator before writing it to CD. For physical media, use a CDI-capable burner and verify the written disc; the required media and writing speed depend on the console, drive, and image.

cdi4dc is generally used in the opposite direction, converting CDI images to BIN/CUE for extraction or preservation; it is not a general MDF-to-CDI converter.

Quality and compatibility limits

There is no dependable, lossless, modern one-click converter for every MDF/MDS variant. A conversion through a mounted drive or extracted files can lose hidden sessions, copy-protection information, raw sectors, audio pregaps, subchannel data, or Dreamcast boot details even when the visible files remain intact.

For archival use, retain the original .mdf/.mds pair and record checksums for both files. Treat the CDI as a compatibility copy, then compare track counts, byte sizes, sector modes, file contents, and boot behavior.

Online converters are generally unsuitable for this format pair. Services that accept MDF commonly produce ISO or another simplified image, may ignore the MDS metadata, and cannot reliably preserve Dreamcast sessions or subchannel data. A desktop application with direct MDS support is safer; do not upload copyrighted or copy-protected disc images to a browser service.