The structure of the AUDIO_PP.IFO is as follows:
|0||12||Identifier string - "DVDAUDIOSAPP"|
|12||2||Total number of tracks on the disk|
|14||2||DVD Specifications Version (0x0012)|
|The following record appears once for each track, sorted by Group and then Track number:|
|+2||1||Group Number (1..9)|
|+3||1||Track Number within Group (1..99)|
|+4||4||Start Presentation Timestamp (PTS) for track. This is the PTS in the AOB file.|
|+8||4||Length of track (in PTS ticks - there are 90000 PTS ticks in one second)|
|+16||4||??Audio format (samplerate and depth) plus other currently unidentified information|
|+40||4||Absolute sector pointer to first sector of AOB for this track|
|+44||4||Absolute sector pointer to first sector of AOB for this track (why is this duplicated?)|
|+48||4||Absolute sector pointer to last sector of AOB for this track|
According to the Sonic DVD White Paper (PDF file) and other sources, a DVD-Audio disk can contain two "content managers". The first is for simple audio-only DVD players (such as portables or in-car units) and according to that white paper, this can store details on up to 314 tracks. This is known as the Simple Audio Manager (SAMG) and contains enough information by itself for full playback of the audio content within the DVD.
The AUDIO_PP.IFO appears to always be exactly 128 kilobytes in size, and contains 8 identical copies of a 16K block of data. This 16K block of data contains a 16 byte header plus one 52 byte record for each track on the DVD. This allows a maximum of 314 records in the 16K block - the same number as mentioned in the above white paper - which implies that the AUDIO_PP.IFO file should be referred to as the Simple Audio Manager (SAMG).