NRG (file format)

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

An NRG file is a proprietary optical disc image file format originally created by Nero AG for the Nero Burning ROM utility. It is used to store disc images. Other than Nero Burning ROM, however, a variety of software titles can use these image files. For example, 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 a .nrg extension and a header attached. They can store audio tracks for Audio CDs, which ISO images cannot. Nero's NRG format is one of the few formats besides BIN/CUE, Alcohol 120%'s MDF/MDS and CloneCD's CCD/IMG/SUB disc image formats to support Mixed Mode CDs which contain audio CD tracks as well as data tracks.

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 32-bit integers. Nero Burning ROM v5.5 introduced a new NRG file format, version 2, with support for 64-bit 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.

Nero footer (Version 1)

Size (bytes)	Type	Value or purpose
4	Chunk ID	"NERO"
4	32-bit	Offset of the first chunk data chain

Nero footer (Version 2)

Size (bytes)	Type	Value or purpose
4	Chunk ID	"NER5"
8	64-bit	Offset of the first chunk data chain

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.

Version 1

Size (bytes)	Type	Value / Purpose
4	Chunk ID	"CUES"
4	32-bit	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

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	8-bit	Padding? (always NULL found)
2	16-bit	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

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

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

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?

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?

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?

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)

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

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)