Convert NRG to CDI

A Dreamcast emulator or legacy DiscJuggler workflow may require a CDI image instead of Nero’s NRG format. Converting can also make an archived optical disc usable without recreating it from physical media.

What the NRG format is

NRG is Nero Burning ROM’s proprietary optical-disc image format. Depending on the NRG version and source disc, it can preserve filesystem data, boot information, sessions, audio tracks, and sector-level CD or DVD structure.

NRG files are found in Nero-created backups, software-disc archives, installation media, and older Windows disc-authoring workflows. An NRG is a sector image, not merely a ZIP-like collection of the files visible on the disc.

What the CDI format is

CDI is the DiscJuggler image format associated with Padus DiscJuggler. It is used mainly for CD images and can describe data tracks, audio tracks, multisession layouts, and raw sectors. CDI files are especially common in older Sega Dreamcast archives and emulators.

CDI is useful only when the target program specifically supports it. It can preserve CD structures that a plain ISO cannot, but it has much poorer support in current software and several CDI variants are not interchangeable.

How to convert NRG to CDI

Recreate the image with DiscJuggler

This is the most direct desktop method when the source contains multiple tracks or Dreamcast-specific sectors.

1. Mount the NRG with a utility that supports Nero images, such as DAEMON Tools, or use a physical disc drive if the NRG has already been written to disc.
2. Open DiscJuggler on Windows and create a new CD-image job from the mounted or physical drive.
3. Select the complete disc as the source and set a destination ending in .cdi. Choose the option for a full-disc or raw-sector read when the software provides one.
4. Start the read and retain the original .nrg until the CDI has been tested.

DiscJuggler is legacy software; it may require an older Windows installation or compatibility settings, and some virtual drives do not expose the raw or subchannel information needed by protected or Dreamcast discs. A CDI made from a mounted image can therefore differ from one made from the original optical disc.

Use a Dreamcast-specific conversion chain

For a Dreamcast image, first convert the NRG to a track-based BIN/CUE representation with a utility such as nrg2cue, provided it supports the NRG variant. Then use cdi4dc or another maintained tool specifically intended to build Dreamcast CDI images from the resulting track data. Follow that tool’s documentation for the required track order, sector mode, and padding.

This route is not a universal NRG-to-CDI converter. It is appropriate only when the source is a compatible Dreamcast CD image and the output tool supports its track layout. Converting through an ordinary ISO can remove audio tracks, boot sectors, multisession data, or raw-sector information.

When an ISO conversion is sufficient

If the image contains only a conventional data filesystem and the target application accepts ISO, convert the NRG to ISO with software such as PowerISO, AnyToISO, or UltraISO. ISO is much more widely supported, but it is not a safe intermediate for mixed-mode, audio, multisession, protected, or Dreamcast images.

Neither renaming image.nrg to image.cdi nor simply changing the extension converts the internal format. IsoBuster can inspect and extract files or tracks from many NRG images, but it is not a general CDI writer.

Online conversion and compatibility limits

No reputable general-purpose online service reliably converts NRG to a CDI that preserves Dreamcast or other raw-disc structures. Browser services that offer NRG conversion commonly produce ISO or extracted files instead; uploading a large disc image also exposes its contents and may exceed service limits. Use a local converter for this format pair.

Compare the CDI’s file size, track count, track types, and sector layout with the source before deleting the NRG. Test the CDI in the intended emulator or DiscJuggler-compatible application. A Dreamcast image that mounts but does not boot may have lost raw sectors or audio tracks, use an incompatible CDI variant, or originate from a non-self-bootable disc.