Oma

• Extension: oma, aa3
• Company: Sony
• Samples: http://samples.mplayerhq.hu/oma/

The OpenMG Audio (further OMA) container format is used to encapsulate digital music content for use with Sony's portable players. Files ending with .omg are protected with the OpenMG DRM system.

The format is known to carry audio streams encoded with:

• ATRAC3
• ATRAC3plus
• ATRAC Advanced Lossless
• MP3
• Linear PCM
• WMA (confirmation required)

File structure

A typical OMA file consists of the following three parts:

• metadata container
• extended audio header
• actual sound data

Metadata container

The metadata container carries overall music info. Except for starting with "ea3" instead of "ID3", it's fully compatible with the ID3v2 format. It uses standard ID3v2 frame types, such as TIT2, TPE1, TALB and TCON. In addition to these standard frame types, TXXX and GEOB frames contain OpenMG-specific metadata.

 TXX   OMG_TRACK  "track number (ASCII)"
 TXX   OMG_AGENR  "content description (ASCII)"
 TXX   OMG_ATPE1  "leader performer (ASCII)"
 GEOB  OMG_BLKSI  contains a metadata structure. observed strings include:
                     KEYRING
                     EKB
                     SHARE_P_SID
                     REFID
 GEOB  OMG_OLINF  binary blob 

Extended audio header

Extended audio header contains information about the encapsulated OpenMG audio. This includes codec type, codec specific info (packet size, sample rate, channels and so on) as well as DRM related info (file encryption, content id).

Sound data

Encrypted or plain-text sound data organized in packets follows the extended audio header.

Further reading

The OMA file format contains a payload scrambled with a 32-bit value [1].