NRG (file format)

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NRG
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
For other uses, see NRG.

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[edit]

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[edit]

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[edit]

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.

Nero footer (Version 1)
Size (bytes) Type Value / Purpose
4 Chunk ID "NERO"
4 32bit Offset of the first chunk data chain
Nero footer (Version 2)
Size (bytes) Type Value / Purpose
4 Chunk ID "NER5"
8 64bit Offset of the first chunk data chain

Chunks[edit]

(CUES) Cue Sheet[edit]

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.

Version 1
Size (bytes) Type Value / Purpose
4 Chunk ID "CUES"
4 32bit Chunk size (bytes)
Version 2
Size (bytes) Type Value / Purpose
4 Chunk ID "CUEX"
4 32bit Chunk size (bytes)
1 8bit Mode (values found: 0x01 for audio; 0x21 for non copyright-protected audio; 0x41 for data)
1 8bit Track number (BCD coded; 0xAA for the lead-out area)
1 8bit Index number (probably BCD coded)
1 8bit Padding? (always zero found)
4 32bit LBA position in sectors (signed integer value)

(DAOI) DAO Information[edit]

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.

Version 1
Size (bytes) Type Value / Purpose
4 Chunk ID "DAOI"
4 32bit Chunk size (bytes) big endian
4 32bit Chunk size (bytes) little endian
14   UPC
4 32bit Toc type
1 8bit First track
1 8bit Last track
12   ISRC
4 32bit Sector size
4 32bit Mode
4 32bit Index0 (Pre gap)
4 32bit Index1 (Start of track)
4 32bit Index2 (End of track + 1)
Version 2
Size (bytes) Type Value / Purpose
4 Chunk ID "DAOX"
4 32bit Chunk size (bytes) big endian
4 32bit Chunk size (bytes) (big endian already encountered; maybe also little endian on some machines)
13 Text UPC (or NULLs)
1 8bit Padding? (always NULL found)
2 16bit Toc type (values already found: 0x0000 for audio; 0x0001 for data; 0x2001 for Mode 2/form 1 data)
1 8bit First track in the session
1 8bit Last track in the session
12 Text ISRC (or NULLs)
2 16bit Sector size in the image file (bytes)
2 16bit Mode of the data in the image file (values already found: 0x0700 for audio; 0x1000 for audio with sub-channel; 0x0000 for data; 0x0500 for raw data; 0x0f00 for raw data with sub-channel; 0x0300 for Mode 2 Form 1 data; 0x0600 for raw Mode 2/form 1 data; 0x1100 for raw Mode 2/form 1 data with sub-channel)
2 16bit Unknown (always 0x0001 found)
8 64bit Index0 (Pre-gap) (bytes)
8 64bit Index1 (Start of track) (bytes)
8 64bit End of track + 1 (bytes)

(CDTX) CD-text[edit]

Available in version 2 nrg file format.

The CDTX chunk is the concatenation of raw CD-text packs of 18 bytes each.

Version 2
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[edit]

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.

Version 1
Size (bytes) Type Value / Purpose
4 Chunk ID "ETNF"
4 32bit Chunk size (bytes)
4 32bit Track offset in image
4 32bit Track length (bytes)
4 32bit Mode
4 32bit Start lba on disc
4    ?
Version 2
Size (bytes) Type Value / Purpose
4 Chunk ID "ETN2"
4 32bit Chunk size (bytes)
8 64bit Track offset in image
8 64bit Track length (bytes)
4 32bit Mode (values found: 0x7 for audio; 0x0 for data; 0x3 for Mode 2 data)
4 32bit Start lba on disc (sectors) (the start is after a lead-in of 150 sectors)
4 32bit Unknown (only zero found)
4 32bit Track length (sectors)

(SINF) Session Information[edit]

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.

Version 1 and 2
Size (bytes) Type Value / Purpose
4 Chunk ID "SINF"
4 32bit Chunk size (bytes)
4 32bit # tracks in session

(MTYP) Media Type?[edit]

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).

Version 1 and 2
Size (bytes) Type Value / Purpose
4 Chunk ID "MTYP"
4 32bit Chunk size (bytes)
4    ?

(DINF) Disc Information?[edit]

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.

Version 2 (and 1?)
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?[edit]

Found in TAO images in version 2 of nrg file format.

This chunk and its use is unknown.

Version 2 (and 1?)
Size (bytes) Type Value / Purpose
4 Chunk ID "TOCT"
4 32bit Chunk size (bytes)
2   Unknown (always zero found)

(RELO)[edit]

Found in TAO images in version 2 of nrg file format.

This chunk and its use is unknown.

Version 2 (and 1?)
Size (bytes) Type Value / Purpose
4 Chunk ID "RELO"
4 32bit Chunk size (bytes)
4   Unknown (always zero found)

(END!) End of chain[edit]

Available in all versions of nrg file format.

End of chain chunk is signals that there are no more chunks to be read.

Version 1 and 2
Size (bytes) Type Value / Purpose
4 Chunk ID "END!"
4 32bit Chunk size (always zero)

See also[edit]

Emulating/editing software supporting NRG[edit]

External links[edit]

  • nrg4isoBSD licensed command line utility. Does not fully support nrg format. Currently abandoned. (POSIX)
  • nrg2isoGPL licensed command line utility. Does not fully support nrg format. (Linux)
  • IATGPL licensed command line utility without support for CD-AUDIO
  • fusenrgGPL 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.