NRG (file format)
| Filename extension |
.nrg |
|---|---|
| Uniform Type Identifier (UTI) | com.nero.nrg-image |
| UTI conformation |
public.iso-image, com.apple.disk-image, public.archive, public.data, public.item, public.disk-image |
| Developed by | Nero AG |
| Type of format | disk image |
| Container for | filesystem and volumes |
A .nrg file is a proprietary CD image file format used by Nero Burning ROM, a utility suite made by Nero AG, to create and burn CD images.
Other than Nero Burning ROM, a variety of software titles can use these image files. For example, PowerISO, Alcohol 120%, or Daemon Tools can mount NRG files onto virtual drives for reading.
Contrary to popular belief, .nrg files are not ISO images with .nrg extension and a header attached.
Converting nrg files
There are several tools available to convert a .nrg data file into an ISO 9660 CD image. Note that converting a cd image .nrg multitrack (data + audio tracks) to ISO involve the loss of audio tracks.
- Open Source command line tools include:
- nrg2iso — cross-platform. Hardcoded to read all nrg files as disc at once (DAO) type causing it to fail on track at once (TAO) type images.
- iat — cross-platform. Tool for detecting the structure of many types of CD/DVD image and convert image CD/DVD to ISO9660.
- fusenrg — for Unix-like systems. Hardcoded to read all nrg files as disc at once (DAO).
- nrg4iso — (project abandoned by author - last updated Oct 2007) for Unix-like systems (including Mac OS X). Can convert both DAO and TAO images into ISO 9660 CD images. Does NOT support DAO with multiple tracks.
- eNeRGy — Mac OS X, based on nrg4iso, has a graphical user interface.
- Shareware tools include:
- PowerISO — converts from nrg to ISO as well as allows for browsing and extracting individual files from a nrg data file.
- MagicIso — Is another powerful tool converts from nrg to ISO as well as allows for browsing and extracting individual files from a nrg data file.
The data contents of NRG files can be extracted directly without creating an ISO image using freeware file archivers such as IZArc.
File format
The file format specification below is unofficial and as such is lacking some data. There may also be errors.
The nrg file format uses a variation of the Interchange File Format (IFF) and stores data in a chain of "chunks". All integer values are stored unsigned in big endian byte order. Version 1 nrg format stores values as 32bit integers. Nero Burning ROM v5.5 introduced a new nrg file format, version 2, with support for 64bit integers.
Header
The nrg format does not store its data as a header at the beginning of a file. It is instead attached at the end of the file like a footer. Image information is stored as a serialized chain of IFF chunks. To get the offset of the first chunk one must read the nrg footer from the last 8 or 12 bytes of the file.
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Chunks
(CUES) Cue Sheet
Available in all versions of nrg file format.
The CUEX chunk is the concatenation of fixed-size blocks, each one representing a cue point.
The index0 points are present even when they are identical to the index1 ones. The index0 points in audio tracks are incorrect if Nero has been asked to record all the sub-channel data (in that case the sector size is 2448 bytes). No index other than 0 or 1 has been encountered, although the chunk format allows for such cue points to be recorded; thus the number of cue blocks seems to be always 2*(#track + 1): two indices for each track, an index0 for the lead-in and an index1 for the lead-out.
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(DAOI) DAO Information
Available in all versions of nrg file format.
DAOI chunks store disc at once sessions specific information in two parts. The first part contains data that is specific for the session only. The second part repeats track specific information (grey) once for each track. Parse the SINF chunks to get the number of tracks for a specific session.
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(CDTX) CD-text
Available in version 2 nrg file format.
The CDTX chunk is the concatenation of raw CD-text packs of 18 bytes each.
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "CDTX" |
| 4 | 32bit | Chunk size (bytes) |
| 1 | 8bit | Pack type |
| 1 | 8bit | Pack type (track number) |
| 1 | 8bit | Pack number in the block |
| 1 | 8bit | Block number etc. |
| 12 | Text | NULL-separated text strings |
| 2 | 16bit | CRC |
(ETNF) Extended Track Information
Available in all versions of nrg file format.
ETNF chunks are used to store track information for track at once sessions. The data is repeated once for each track. Parse the SINF chunks to get the number of tracks for a specific session.
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(SINF) Session Information
Available in all versions of nrg file format.
Session information chunks should be used to quickly scan the image for session and track count. SINF chunks are always listed in sequential order corresponding to the sessions order. To get more details information about a specific session one must parse the corresponding DAOI or ETNF chunk.
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "SINF" |
| 4 | 32bit | Chunk size (bytes) |
| 4 | 32bit | # tracks in session |
(MTYP) Media Type?
Available in all versions of nrg file format.
This chunk and its use is unknown. A value of 1 (big endian) was found in images of several CD (audio or data; CD-ROM or CD-R).
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "MTYP" |
| 4 | 32bit | Chunk size (bytes) |
| 4 | ? |
(DINF) Disc Information?
Found in TAO images in version 2 of nrg file format. Found in DAO images in version of nrg file format only if Nero was asked not to close the disc.
This chunk and its use is unknown.
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "DINF" |
| 4 | 32bit | Chunk size (bytes) |
| 4 | 32bit | Unknown (found 0x1 for an unclosed disc; 0x0 otherwise) |
(TOCT) TOC T?
Found in TAO images in version 2 of nrg file format.
This chunk and its use is unknown.
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "TOCT" |
| 4 | 32bit | Chunk size (bytes) |
| 2 | Unknown (always zero found) |
(RELO)
Found in TAO images in version 2 of nrg file format.
This chunk and its use is unknown.
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "RELO" |
| 4 | 32bit | Chunk size (bytes) |
| 4 | Unknown (always zero found) |
(END!) End of chain
Available in all versions of nrg file format.
End of chain chunk is signals that there are no more chunks to be read.
| Size (bytes) | Type | Value / Purpose |
|---|---|---|
| 4 | Chunk ID | "END!" |
| 4 | 32bit | Chunk size (always zero) |
See also
- Disk image
- DMG (Apple disk image)
- ISO image
Emulating/editing software supporting NRG
External links
- nrg4iso — BSD licensed command line utility. Does not fully support nrg format. Currently abandoned. (POSIX)
- nrg2iso — GPL licensed command line utility. Does not fully support nrg format. (Linux)
- IAT — GPL licensed command line utility without support for CD-AUDIO
- fusenrg — GPL licensed command line utility. Converts NRG to ISO on the fly. Does not fully support nrg format. (Linux)
- nrg2iso — Windows graphical utility. Does not fully support nrg format. (Windows)
- IMGBURN — Windows Freeware ISO burning software capable of managing the nrg format.
- eNeRGy' — GPL Mac OS X utility, based on nrg4iso, has a graphical user interface
- nrgtoiso — Windows Freeware graphical utility. Converts nrg format to iso format.
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