This is the metadata file that ends in ".cnmt{.nca}" or "meta0.ncd". This seems to replace the TMD format.

The official name for CNMT is "PackagedContentMeta".

PackagedContentMetaHeader

This is "nn::ncm::PackagedContentMetaHeader".

Offset Size Description
0x0 0x8 Id
0x8 0x4 Version
0xC 0x1 ContentMetaType
0xD 0x1 Reserved
0xE 0x2 ExtendedHeaderSize
0x10 0x2 ContentCount
0x12 0x2 ContentMetaCount
0x14 0x1 ContentMetaAttributes (0=None, 1=IncludesExFatDriver, 2=Rebootless, 4=Compacted)
0x15 0x3 Reserved
0x18 0x4 RequiredDownloadSystemVersion
0x1C 0x4 Reserved

SystemUpdateMetaExtendedHeader

This is "nn::ncm::SystemUpdateMetaExtendedHeader".

Offset Size Description
0x0 0x4 ExtendedDataSize

ApplicationMetaExtendedHeader

This is "nn::ncm::ApplicationMetaExtendedHeader".

Offset Size Description
0x0 0x8 PatchId
0x8 0x4 RequiredSystemVersion
0xC 0x4 RequiredApplicationVersion

PatchMetaExtendedHeader

This is "nn::ncm::PatchMetaExtendedHeader".

Offset Size Description
0x0 0x8 ApplicationId
0x8 0x4 RequiredSystemVersion
0xC 0x4 ExtendedDataSize
0x10 0x8 Reserved

AddOnContentMetaExtendedHeader

This is "nn::ncm::AddOnContentMetaExtendedHeader".

Offset Size Description
0x0 0x8 ApplicationId
0x8 0x4 RequiredApplicationVersion
0xC 0x1 [15.0.0+] ContentAccessibilityIndividual ([1.0.0-14.1.2] Reserved)
0xD 0x3 Reserved
0x10 0x8 [15.0.0+] DataPatchId

DeltaMetaExtendedHeader

This is "nn::ncm::DeltaMetaExtendedHeader".

Offset Size Description
0x0 0x8 ApplicationId
0x8 0x4 ExtendedDataSize
0xC 0x4 Reserved

DataPatchMetaExtendedHeader

This is "nn::ncm::DataPatchMetaExtendedHeader".

This was added with [15.0.0+].

Offset Size Description
0x0 0x8 DataId
0x8 0x8 ApplicationId
0x10 0x4 RequiredApplicationVersion
0x14 0x4 ExtendedDataSize
0x18 0x8 Reserved

PackagedContentInfo

This is "nn::ncm::PackagedContentInfo".

Offset Size Description
0x0 0x20 Hash (SHA256 of the referenced content)
0x20 0x10 ContentId
0x30 [15.0.0+] 0x5 ([1.0.0-14.1.2] 0x6) Size
0x35 0x1 [15.0.0+] ContentAttributes
0x36 0x1 ContentType (0=Meta, 1=Program, 2=Data, 3=Control, 4=HtmlDocument, 5=LegalInformation, 6=DeltaFragment)
0x37 0x1 IdOffset

ContentMetaInfo

This is "nn::ncm::ContentMetaInfo".

Offset Size Description
0x0 0x8 Id
0x8 0x4 Version
0xC 0x1 ContentMetaType
0xD 0x1 ContentMetaAttributes (0=None, 1=IncludesExFatDriver, 2=Rebootless, 4=Compacted)
0xE 0x2 Reserved

This is used for SystemUpdate, see here: NCM_services#ReadEntryMetaRecords.

SystemUpdateMetaExtendedData

This is "nn::ncm::SystemUpdateMetaExtendedData".

If the Version field is 1, the format is:

Offset Size Description
0x0 0x4 Version
0x4 0x4 VariationCount
0x8 0x20 * VariationCount FirmwareVariationInfo (Version 1)

If the Version field is 2, the format is:

Offset Size Description
0x0 0x4 Version
0x4 0x4 VariationCount
0x8 0x4 * VariationCount FirmwareVariationId
Variable 0x20 * VariationCount FirmwareVariationInfo (Version 2)
Variable 0x10 * MetaCount (from FirmwareVariationInfo (Version 2)) ContentMetaInfo (if ReferToBase is False)

FirmwareVariationInfo

This is "FirmwareVariationInfo ".

If the Version field is 1, the format is:

Offset Size Description
0x0 0x4 FirmwareVariationId
0x4 0x1C Reserved

If the Version field is 2, the format is:

Offset Size Description
0x0 0x1 ReferToBase (0=False, 1=True)
0x1 0x3 Reserved
0x4 0x4 MetaCount
0x8 0x18 Reserved

PatchMetaExtendedData

This is "nn::ncm::PatchMetaExtendedData".

Offset Size Description
0x0 0x4 PatchHistoryHeaderCount
0x4 0x4 PatchDeltaHistoryCount
0x8 0x4 PatchDeltaHeaderCount
0xC 0x4 FragmentSetCount
0x10 0x4 PatchHistoryContentInfoCount
0x14 0x4 PatchDeltaPackagedContentInfoCount
0x18 0x4 Reserved
0x1C 0x38 * PatchHistoryHeaderCount PatchHistoryHeader
Variable 0x28 * PatchDeltaHistoryCount PatchDeltaHistory
Variable 0x28 * PatchDeltaHeaderCount PatchDeltaHeader
Variable 0x34 * FragmentSetCount FragmentSet
Variable 0x18 * PatchHistoryContentInfoCount PatchHistoryContentInfo (PackagedContentInfo without the Hash entry)
Variable 0x38 * PatchDeltaPackagedContentInfoCount PatchDeltaPackagedContentInfo
Variable 0x4 * FragmentIndicatorCount (from FragmentSet) FragmentIndicator

PatchHistoryHeader

This is "nn::ncm::PatchHistoryHeader".

Offset Size Description
0x0 0x10 ContentMetaKey
0x10 0x20 Digest
0x30 0x2 ContentInfoCount
0x32 0x6 Reserved

PatchDeltaHistory

This is "nn::ncm::PatchDeltaHistory".

Offset Size Description
0x0 0x8 SourcePatchId
0x8 0x8 DestinationPatchId
0x10 0x4 SourceVersion
0x14 0x4 DestinationVersion
0x18 0x8 DownloadSize
0x20 0x8 Reserved

PatchDeltaHeader

This is "nn::ncm::PatchDeltaHeader".

Offset Size Description
0x0 0x8 SourcePatchId
0x8 8 DestinationPatchId
0x10 0x4 SourceVersion
0x14 0x4 DestinationVersion
0x18 0x2 FragmentSetCount
0x1A 0x6 Reserved
0x20 0x2 ContentInfoCount
0x22 0x6 Reserved

FragmentSet

This is "nn::ncm::FragmentSet".

Offset Size Description
0x0 0x10 SourceContentId
0x10 0x10 DestinationContentId
0x20 0x6 SourceSize
0x26 0x6 DestinationSize
0x2C 0x2 FragmentIndicatorCount
0x2E 0x1 FragmentTargetContentType (0=Meta, 1=Program, 2=Data, 3=Control, 4=HtmlDocument, 5=LegalInformation, 6=DeltaFragment)
0x2F 0x1 UpdateType (0=ApplyAsDelta, 1=Overwrite, 2=Create)
0x30 0x4 Reserved

FragmentIndicator

This is "nn::ncm::FragmentIndicator".

Offset Size Description
0x0 0x2 ContentInfoIndex
0x2 0x2 FragmentIndex

DeltaMetaExtendedData

This is "nn::ncm::DeltaMetaExtendedData".

Offset Size Description
0x0 0x8 SourcePatchId
0x8 0x8 DestinationPatchId
0x10 0x4 SourceVersion
0x14 0x4 DestinationVersion
0x18 0x2 FragmentSetCount
0x1A 0x6 Reserved
0x20 0x34 * FragmentSetCount FragmentSet
Variable 0x4 * FragmentIndicatorCount (from FragmentSet) FragmentIndicator

Digest

Always found at the end of the file.

Offset Size Description
0x0 0x20 Digest