In addition to the Simple Audio Manager (SAMG) stored in the AUDIO_PP.IFO file, there is a second audio manager stored on a DVD-Audio disk known as the Audio Manager (AMG). This is the information stored in the AUDIO_TS.IFO file.
In a so-called "Universal" or "Hybrid" disc, the AMG will contain pointers to Video IFO files located in the VIDEO_TS zone on the disk. My understanding is that a DVD-Audio player will use the Audio Manager (AMG - AUDIO_TS.*) to control playback (using both ATS and VTS files), and that a DVD-Video only player will use the Video Manager (VMG - VIDEO_TS.*) to control playback (using only the VTS files).
The AMG consists of the AUDIO_TS.IFO file, optionally followed by an AUDIO_TS.VOB file, followed by the backup AUDIO_TS.BUP file.
The structure and contents of the AUDIO_TS.IFO is very similar to a VIDEO_TS.IFO file and is as follows:
|0||12||Identifier string - "DVDAUDIO-AMG"|
|12||4||Relative sector pointer to last sector in AMG (i.e. the last sector of AUDIO_TS.BUP)|
|28||4||Relative sector pointer to last sector in AMGI (i.e. the last sector of AUDIO_TS.IFO)|
|32||2||DVD Specifications Version (0x0012)|
|38||2||Number of Volumes (0x0001)|
|40||2||Current Volume (0x0001)|
|42||1||Disc Side (0x01)|
|47||1||??? (0x01 on a disk without SV, 0x00 on a disk with SV)|
|48||4||Relative sector pointer from end of AUDIO_TS.IFO to start of AUDIO_SV.IFO, zero if there is no AUDIO_SV.IFO on the disk|
|62||1||Number of video titlesets|
|63||1||Number of audio titlesets|
|64||32||Unknown (zero) - "Provider ID" in VIDEO_TS.IFO|
|96||8||Unknown (zero) - "VMG Position Code" in VIDEO_TS.IFO|
|128||4||End Byte Address of AMGI_MAT (0x07ff) - i.e. the end byte of this block of data|
|132||4||Unknown (zero) - "First-Play PGC Start Byte" in VIDEO_TS.IFO|
|TO DO: More data exists if there are still images or an AUDIO_TS.AOB. However, it is all zero if those elements don't exist.|
The second and third sectors both contain very similar tables. For disks without a Video Zone, both tables are identical, if there is a linked Video Zone, then the second sector contains pointers to both ATS and VTS titles, but the third sector only contains pointers to ATS titles.
|0||2||Number of titles|
|2||2||Byte pointer to last byte of data in this table (e.g. 0x0057 to indicate the last byte is at 0x0857 in this file)|
|The following table repeats once for each titleset|
|0||1||High nibble: ??? 0x8 for ATS, 0x4 for VTS|
Low nibble: Titleset number???
|1||1||Number of tracks in title|
|4||4||Total length of title (in PTS ticks)|
|9||1||Title number within titleset|
|10||4||Relative sector pointer to ATSI (i.e. from start of AUDIO_TS.IFO to start of relevant ATS_XX_0.IFO)|
Information concerning the AUDIO_TS.VOB file (and possibly the still pictures) are in the subsequent sectors. These sectors are not yet documented.