Oblivion Mod:Save File Format/ACHR Uncertainties

This article summarizes uncertain information about the ACHR and ACRE change records.

Overview

Known record storing orders
Consult Locations of Subrecords for certain locations and Appearance of Subrecords table below to get an overview of currently known record storing order.

The Actor Flag is a one byte flag. It has following known states:

• 0 - High
• 1 - Mid High
• 2 - Mid Low
• 3 - Low
• FF - None.
  

It seems that the Actor Flag defines the role of an NPC actor and the appearance of subrecords in the ACHR record. There are named subrecords like Scale, Run Once and so on triggered by the records general flags and subrecords or sections with coded names that seems to be presented as two byte hex values. For instance in different ACHR records of NPC high actors there can be found subrecords with hex codes 0x803F, 0x80BF or 0x3036 at fix locations. Meaning is unknown. Inside often found references (iref) and or values(float).

Some named subrecords can be found in a structure containing flags and corresponding sets of values. It is suggested to be the Actor Properties structure and describes changed essential actor properties. Consult Properties for detailed information.

Some change records internal formats are still unknown. At best you can see here:

1. Is change record's length constant or variable.
2. Flags that are indicating change record's existence in the record.
   • If there is more than one flag, then it is possible that there multiple flags indicating change record - or there wasn't enough data to find single flag.
   • It is also possible that multiple change records are sharing same flags or change records are actually same record - they just have different name in dump file.
3. Change record's minimal and maximal lengths.
4. Possible substructures lengths inside change record. This length is largest common divider from all change records minimal and maximal lengths.

Appearance of Subrecords depending on Actors Role

Table describes appearance of subrecords depending on the state of the Actor Flag. This table is very speculative but provides currently a usable understanding of subrecord locations that helps to walk through a ACHR change record. Subrecord names with unknown meaning but fix locations are represented by their hex-values. Some other have only suggested names because it is unknown where they belong to.

How to read the table:

• a row filled with Aquamarine color means that the subrecord appears when the records general change flag is set
• a colored cell under the Actor Flag name means that the subrecord appears only when the corresponding flag is set

Name	Type	Size [bytes]	Info	High	MidHigh	MidLow	Low	None
Cell Changed	struct	16
Created	struct	36
Moved	struct	28
Actor Flag	byte	1	flag
Form Flag	ulong	4
Temporary Attribute Changes	struct	876	present only if PC record (0x14)
Inventory	struct
Actor Properties	struct[num]
Havok Moved	struct[size]
Scale	float	4
Dialogue/Mount Horse	struct
Active Pack Data	struct
0x362e/0x3630/0x3646		32
Game Modifier	struct[num]
unknown		9
Magic Modifier	struct[num]
unknown		6/5/2/0	?depends on actorFlag?
0x3F80		6
Run Once	FormID	4
unknown		25
0xFFFF		34	?0xff ff 00 7f in every save file?
0x3F80		18	also 0x3FB3, 0x3F8C, 0x3F86
Animation #1	struct
Unknown Struct	struct[num]		{{size, iref, flag, data[size]}, ... }
Divider		19	usually 0x1, ?belongs to Anim #1?
Divider		84	always present (0x1)
0x3F80		40
Unknown Struct	struct[num]		{{byte[13}, ... } ?thrown inventory items?
0x4CFF/0x4C03/0x58FF		77/77/87
0x3F80		74
Common Divider #1	flag	1	usually 0x1, common means it is a flag at a fix location for all records
Life State	flag	1
Disposition Modifier	struct[num]
Equipment	ulong	4	meaning unknown
Indicator	short	2	belongs to Common Divider #1: Indicator = 0x0 and Com Div #1 = 0, than skip 4 bytes and Com Div #1 = 1, than skip 8 bytes Indicator = 0x1 skip 16 Indicator = 0x100 skip 17byte
Script Modifiers	struct[num]
unknown		17/8	skip 17 bytes if Actor Flag not 0xFF (None)
Common Divider #2	flag	1	Usually 0x1 PC record (0x14): always skip 38 bytes to reach PC section NPC record: skip 9 + 2 bytes till records end
PC section			present only if PC record (0x14)

Active Package Data

The interpretation of this subrecord is very speculative. It is not backed up by text file dumps and its meaning is deduced from found data inside this subrecord.
The subrecord is present for all type of actors. Its length is minimum 17 bytes except for None- actors where it has a fix length 6 bytes.
It is suggested that the subrecord stores the coordinate offset from a package's target reference point along with a flag that describes the state of the current package.

Name	Type/Size	Info
-AI Pack	iref	actually it appears and is an iref that points to a PACK only if the read number is greater than two otherwise it is the type (see next row), other conditions where not found
type	ulong	seems to be related to property flag 0x1f, see Properties
X	float	coordinate offset
Y	float	coordinate offset
Z	float	coordinate offset
flag	ubyte	unknown
None - Actor
value	float
unknown	ushort

Life State (6)

This change record is used in ACHR, ACRE record types.

Name	Type/Size	Info
state	ubyte	Enum: 0 = Alive 1 = Dying 2 = Dead 3 = Unconscious 4 = ? 5 = ? 6 = ?

Disposition Modifiers (15)

Entries in this subrecord are modifying an actors disposition towards another NPC.

This change record is used in ACHR, ACRE record types.

Name	Type/Size	Info
num	ushort	length of sub structure array
dispModifiers	struct[count]
reference	iref	points to an actor (ACHR)
modifier	ulong	value added to initial disposition

Movement Blocked (17)

This change record's length is constant 32 byte(s).

This change record is used in ACHR, ACRE record types. There was 14 change records in save files.

This information is NOT verified from actual save files.

Name	Type/Size	Info
unknown	ubyte[32]	Constant length of observed change records.

Run Once (19)

This change record's length is constant 22 byte(s).

This change record is used in ACHR, ACRE record types. There was 6 change records in save files.

This information is NOT verified from actual save files.

Name	Type/Size	Info
unknown	ubyte[22]	Constant length of observed change records.

Magic Modifiers (20)

Entries in this subrecord are modifying base actor values. They are used for temporary and dispellable magic effects.

Despite the fact that there is a counter for the amount of entries the sub structure array never contains only one entry. There will be zero entries (number equals zero) or not less than two entries.

This change record is used in ACHR, ACRE record types.

Name	Type/Size	Info
num	ushort	length of sub structure array
magModifiers	struct[num]	collection of modified actor values
index	ubyte	base actor value that is modified, see Actor Value Indices
value	float	modifier added to base actor value

Script Modifiers (21)

Entries in this subrecord are modifying base actor values. They are used for temporary and non-dispellable scripted effects.

This change record is used in ACHR, ACRE record types.

Name	Type/Size	Info
num	ushort	length of substructure array
scriptModifiers	struct[num]	collection of modified actor values
index	ubyte	base actor value that is modified, see Actor Value Indices
value	float	modifier added to base actor value

Game Modifiers (22)

Entries in this subrecord are modifiers to base actor values. They are used for permanent effects.

This change record is used in ACHR, ACRE record types.

Name	Type/Size	Info
num	ushort	length of struct
gameModifiers	struct[num]	collection of modified actor values
index	ubyte	base actor value that is modified, see Actor Value Indicies
value	float	modifier added to base actor value

Animation (25)

Part of properties section. See Properties, specifically flag 0x4a.

Animation data seems to be divided into two parts. For all records, if triggered by records flags, there is the Animation 3rd Person view section. Only for the PC change record (0x14) there exists a second part and this is probably the first person view data. In PC change record both parts are not connected. There is a defined gap in between filled with other data. It seems that the type of the current animation (Action, Idle) is described with special codes and only values of some variables are stored.

This change record is used in ACHR, ACRE, REFR record types.

This information was found in a couple of actual save files.

Name	Type/Size	Info
Animation 3rd Person
animName	ushort	?type of animation?
list()		list, terminates with 0x0000
animCode	ushort	defines structure of data
dataStruct	different	animation control data
...		next animation data code
...		next animation data
0x0	ushort	indicates end of list
parent	iref	reference to parent animation (bench, bed)
animCode: 0x0022	ushort	optional, only if parent not 0
dataStruct #2
...
gap		other data
...
Animation 1st Person		appears only within PC's ACHR change record
animName	ushort	?type of animation?
list()		list, terminates with 0x0000
animCode	ushort	defines structure of data
dataStruct	different	animation control data
...		next animation data code
...		next animation data
0x0	ushort	indicates end of list
dataStruct #3		no animation code, always there
unknown	byte[35]	unknown animation data

Animation names

Meaning of animation names are unknown.

Name	Info
0x01ff
0x05ff
0x09ff
0x11ff
...

Animation Data Codes

Meaning of codes are unknown.

Name	Type/Size	Dependent Data Structure	Info
0x0100	ushort	1
0x0115	ushort	1
0x0029	ushort	1
0x0000	ushort	1
0x0021	ushort	1
0x0022	ushort	2
...

Data Structure

Only loop time variables are verified from in-game debug tables. All other are guessed.

Number	Name	Type/Size	Info
1	unknown	int	?
	unknown	byte[11]	?
	time	float	?loop time?
	unknown	int	?
	time	float	?loop time?
	time	float	?loop time?
	unknown	int	?always 0xff 7f ff ff?
2	unknown	int	?
	unknown	int	?
	unknown	int	?
	unknown	ushort	?code?
	time	float	?
	unknown	int	?
	time	float	?
	time	float	?
	unknown	int	?
3	unknown	int	?
	unknown	int	?
	unknown	int	?
	time	float	?
	time	float	?
	time	float	?
	unknown	int	?

Dialogue, Mount Horse, Follow

It is suggested that this subrecord defines the procedure of the current AI package of an NPC actor. Text file dumps from save files include a formid with the subrecord special names. Except for the named Dialogue subrecord there is encountered a fix length of 32 bytes.
The Dialogue subrecord seems to appear when two NPC actors are in a conversation. For one actor the subrecords length will be 5 bytes (formid and type flag). This can be recognized by simultaneously set 'Non-saved-Package' flag. The other conversation partner will have a full data section with used topic texts and paths to voice files along with a data section containing reference to the targeted actor.

This change record is used in ACHR, ACRE, REFR record types.

Name	Type/Size	Info
reference	formid	seems to be an in game created record (0xFF...)
flag	ubyte	0x12 - Dialogue 0x16 - Mount Horse
type1	ubyte	0x4 - horse data 0x6 - target data
type2	ubyte	0x8 - topic data
size	ushort	size of target data section, if Dialogue subrecord else it is zero
Dialogue
targetData	struct[size]
size	ushort	overall size of topic data section
num	ushort	Number of subrecords
topicData	struct[num]
flag	ubyte	mostly 0x1
text	bstring	used topic text
path	bstring	relative path to voice file
unknown	struct[25]
indicator	ushort	always 0x0, ?terminates subrecord?
Mount Horse
unknown	struct[23]

Equipment (29)

This change record is used in ACHR record types.

Name	Type/Size	Info
hash	ulong