PSA File Format

Overview

PSA and PSK binary files contain the raw animation and mesh information used to import skeletal animation art into the Unreal engine. The PSA file contains the bone names, one or more sequence names, and for each sequence, its frame number N, and tracks of N rotations and N translations for each bone. In Mass Effect 3, PSA data is included inside PCC files and can be exported using the PCC Editor tool integrated in ME3Explorer. To learn how to export and edit PSA data from ingame files read the PSA Editing Tutorial. This page will be concerned with the specifcs of the PSA binary format.

File Structure

The PSA file is structured as a collection if header-data pairs, of which there are four known types: Head, Bones, Info, Keys.

Schematic representation of a PSK file structure.

Chunk Header

The chunk header contains information about its companion data chunk: ID, type, size and count. There are four possible IDs, corresponding to each of the eight mesh objects:

• ANIMHEAD: Does not contain a data pair.
• BONENAMES: Array with the bone names.
• ANIMINFO: Array of animation sequence info chunks.
• ANIMKEYS: Array of raw keys.

The header is contained within a 32 byte struct:

Bytes	Type	Description
20	Char	Chunk ID
4	Int32	Type Flag
4	Int32	Data Size
4	Int32	Data Count

Head

The head data chunk is defined by its header as having zero size and zero elements (count). Since it contains no information, it derives that only the header chunk has useful meaning. The header chunk may act as a file-header, but does not necessarily have to be the first chunk in the file.

Bones

The bones data chunk contains an array of bone names. Each bone is defined as a 100 bytes struct.

Bytes	Type	Description
64	Char	Bone name
4	Int32	Flags
4	Int32	Children
4	Int32	Parent index
4	Float	Rotation X
4	Float	Rotation Y
4	Float	Rotation Z
4	Float	Rotation W
4	Float	Position X
4	Float	Position Y
4	Float	Position Z
16	4 * Int32	Padding

Info

The info data chunk contains an array of animation sequence info chunks. Each sequence is defined as a 228 bytes struct.

Bytes	Type	Description
64	String	Sequence name
64	String	Sequence group
4	Int32	Bone count
4	Int32	Root include
4	Int32	Compression style
4	Int32	Key quotum
4	Float	Key reduction
4	Float	Track time
4	Float	Animation rate
4	Int32	Start bone
4	Int32	First raw frame
4	Int32	Raw frame count

Keys

The raw key array holds all the keys for all the bones in all the specified sequences. For each info sequence in the Info array, there are [bones count] * [frames keys count]. These are in turn laid out as tracks of [frame count] keys for each bone in the order of the bones, as defined in the Bones data array.

Bytes	Type	Description
4	Float	Location X
4	Float	Location Y
4	Float	Location Z
4	Float	Rotation X
4	Float	Rotation Y
4	Float	Rotation Z
4	Float	Rotation W
4	Float	Time

ME3Explorer Classes

ME3Explorer > PSAViewer > PSAViewer.cs
ME3Explorer > Unreal > PSAFile.cs

References

• EpicGames page on binary format specifications for skeletal and vertex animation source files
• Gildor's ActorX Importer
• ME3Explorer Forum Discussion: PSK File Format