FF7/PSX/Sound/AKAO sequence

Introduction

AKAO frames are most complicated frames in FF7 sound system. ("AKAO" is frame magic, probably developed by Minoru Akao, Square Enix sound programmer :) )

Frame is similar to MIDI sequence - it's custom tracker format for playing sequence sound, well tuned specially for PSX.

This frames are in all FF7 game modules: Field, Battle, Worldmap and in minigames.

All files with exension *.SND are AKAO.

MINI/ASERI2.SND - Battle Arena theme

MINI/SENSUI.SND - used in Submarine minigame

ENEMY6/OVER2.SND - game over sequence

ENEMY6/FAN2.SND - battle win "fanfare" sequence

MOVIE/OVER2.SND - same game over sequence, don't know, why to duplicate data

Other AKAO frames are hard-wired in other files.

AKAO frame structure

Header (size: 16 bytes)

struct AkaoHeader
{
  static const uint8_t magic[4];  // "AKAO" C-string aka frame *MAGIC*
  uint16_t id;                    // frame ID, used for playing sequence
  uint16_t length;                // frame length - sizeof(header)
  uint16_t reverb_type;           // reverb type (range from 0 to 9)
  struct AkaoTimeStamp timestamp; // some numbers, can't find their usage
};

struct AkaoTimeStamp
{
  uint8_t year_bcd;    // year (in binary coded decimal)
  uint8_t month_bcd;   // month (in binary coded decimal, between 0x01 - 0x12)
  uint8_t day_bcd;     // day (in binary coded decimal, between 0x01 - 0x31)
  uint8_t hours_bcd;   // hours (in binary coded decimal, between 0x00 - 0x23)
  uint8_t minutes_bcd; // minutes (in binary coded decimal, between 0x00 - 0x59)
  uint8_t seconds_bcd; // seconds (in binary coded decimal, between 0x00 - 0x59)
}

Channel info (size: 4 bytes + 2 bytes * <channels count>)

First there is 32-bit number (offset 0x10), which represents bitmask of used channels in this frame, after this frame there is <channels count> offsets to channel opcode data counting from current offset.

Channel Commands [AKAO Opcodes]

Most complicated part.

For every channel in AKAO frame there is set of commands to perform. This is similar to Field opcodes. Here I'll call this sound commands "opcodes". Every opcode has it's own number of arguments (from no-arguments, to 3 arguments).