AEP layers

Each layer of a composition is one list inside the composition’s LIST:Item: LIST:Layr for the layers a user sees, and LIST:SLay, LIST:CLay, LIST:DLay and LIST:SecL for the view layers After Effects keeps for every composition (the 3D view cameras and the composition markers). All of them have the same shape. Everything a layer animates hangs off its root property group, described on Properties and keyframes. This page follows the py_aep specification; Adobe publishes no description of the format.

Children of a layer list

In the order After Effects writes them, in every sample from AE CC 2018 to AE 2026:

Child	Occurs	Meaning
`ldta`	1, required	Layer record: ID, timing, switches, type and parent.
`Utf8`	1, required	Layer name in UTF-8, any length. Empty means the layer shows its source item’s name.
`LIST:tdgp`	1, required	The root property group.
`LIST:Gide`	1	Layer guides, usually empty.
`cmta`	0–1	Layer comment.
`LIST:OvdG`	0–1	Essential Graphics overrides.
`mdla`, `mdlv`	0–1 each	3D model layers only, after `LIST:Gide`.

ldta: layer record (160 or 164 bytes)

The record is 160 bytes in files whose version is below 94 and 164 bytes from file version 94 (AE 2023) on. A 164-byte record in an older file makes every version of After Effects refuse the composition. Times are a dividend and a divisor (seconds = dividend ÷ divisor). The in and out points are in layer time: they are measured from the layer’s start and are not stretched, so the in point in the composition is start time + in point × stretch ÷ 100, and the same for the out point.

Offset	Size	Type	Name	Meaning
0x00	4	u4	Layer ID	Unique and persistent; parent and matte fields and `tdpi` refer to it. Drawn from the same counter as item IDs.
0x04	2	u2	Quality	0 Wireframe, 1 Draft, 2 Best. Cameras, lights and view cameras store 0.
0x06	2	bytes		0 in the samples.
0x08	4	s4	Stretch	Dividend; the divisor is at 0x6C. Stretch in per cent = 100 × dividend ÷ divisor. Negative means the layer plays backwards.
0x0C	4	s4	Start time	Dividend, in composition time.
0x10	4	u4	Start time	Divisor, usually 600 or the composition timebase.
0x14	4	s4	In point	Dividend, in layer time.
0x18	4	u4	In point	Divisor, usually the composition timebase.
0x1C	4	s4	Out point	Dividend, in layer time.
0x20	4	u4	Out point	Divisor.
0x24	1	u1		0 in the samples.
0x25	1	u1	Flags A	See below.
0x26	1	u1	Flags B	See below.
0x27	1	u1	Flags C	See below. Usually 0x07 on AV layers and nulls, 0x87 on text and shape layers, 0x01 on cameras and lights.
0x28	4	u4	Source	The `idta` ID of the footage, solid or composition. 0 for text, shape and camera layers. Lights store 0 up to AE 2022 and `0xFFFFFFFF` from AE 2023, except an environment light that uses a footage item, which stores its ID.
0x2C	15	bytes		0 in the samples.
0x3B	1	u1		Unknown. 1 on every AV layer (footage, solid, null, text, shape, 3D model, mesh), 0 on cameras, lights and view cameras.
0x3C	1	u1		Unknown. Usually 0; 1 on a few layers, 3D nulls among them.
0x3D	1	u1	Label	Label colour, 0 (none) to 16.
0x3E	2	bytes		0 in the samples.
0x40	32	char[32]	Short name	The first 31 bytes of the layer name, NUL-terminated. The `Utf8` that follows is authoritative; older files may hold this copy in an 8-bit legacy encoding.
0x60	3	bytes		0 in the samples.
0x63	1	u1	Blending mode	See below.
0x64	3	bytes		0 in the samples.
0x67	1	u1	Transfer flags	Bit 0 preserve underlying transparency; bit 1 Dancing Dissolve (with blending mode 3).
0x68	3	bytes		0 in the samples.
0x6B	1	u1	Track matte	0 none, 1 Alpha, 2 Alpha Inverted, 3 Luma, 4 Luma Inverted.
0x6C	4	u4	Stretch	Divisor.
0x70	8	f8		0.0 in the samples.
0x78	8	f8		0.0 in the samples.
0x80	3	bytes		0 in the samples.
0x83	1	u1	Layer type	See below.
0x84	4	u4	Parent	Parent layer ID; 0 for none.
0x88	3	bytes		0 in the samples.
0x8B	1	u1	Subtype	Light type on a light, mesh type on a parametric mesh, otherwise 0.
0x8C	4	u4		1 on the six secondary view cameras (`LIST:SLay`), otherwise 0.
0x90	1	u1	View layer	1 on every view layer (`SLay`, `CLay`, `DLay`, `SecL`), 0 on composition layers.
0x91	3	bytes		0 in the samples.
0x94	4	u4		1 when 0x98 is not zero, otherwise 0.
0x98	8	f8		0.0, 36.0 or 102.047… on cameras and view cameras, 0.0 elsewhere. Inferred to be a 36 mm film size (102.047 = 36 × 72 ÷ 25.4).
0xA0	4	u4	Matte layer	Track matte layer ID, 0 for none. Only in the 164-byte record; before AE 2023 the matte was always the layer above.

A stretch set from a script is stored as the exact ratio of the 32-bit float of the percentage ÷ 100 (133.33 % is 11184531 ÷ 8388608), and anything under 1 % becomes 655 ÷ 65536. A time-reversed layer’s time 0 sits |stretch| ÷ 100 ÷ 3000 seconds before its start time.

Layer flags

Flags A (0x25)

Bit	Mask	Meaning
0	0x01	The name was set on a layer that has a source item. Always 0 on layers without a source (camera, light, text, shape), except a renamed parametric mesh.
1	0x02	Guide layer.
2	0x04	Frame blending type: 1 Pixel Motion, 0 Frame Mix. Only meaningful with flags C bit 4.
3	0x08	Per-character 3D.
4	0x10	Auto-orient characters towards the camera (needs bit 3).
5	0x20	Environment layer.
6	0x40	Sampling quality: 1 Bicubic, 0 Bilinear.
7	0x80	0 in the samples.

Flags B (0x26)

Bit	Mask	Meaning
0	0x01	Auto-orient along path.
1	0x02	Adjustment layer.
2	0x04	3D layer.
3	0x08	Solo.
4	0x10	Layer markers locked (inferred).
5	0x20	Auto-orient towards the camera, on an AV layer (needs bit 2).
6	0x40	Auto-orient towards the point of interest, on a camera or light (two-node). AE 2026 writes 0x44 for a default two-node camera.
7	0x80	Null layer.

Flags C (0x27)

Bit	Mask	Meaning
0	0x01	Video enabled.
1	0x02	Audio enabled.
2	0x04	Effects active.
3	0x08	Motion blur.
4	0x10	Frame blending on (type in flags A bit 2).
5	0x20	Locked.
6	0x40	Shy.
7	0x80	Collapse transformations, or continuously rasterise.

Auto-orient is spread over three bits: along path is flags B bit 0; towards the camera is flags B bit 5 on AV layers or bit 6 on cameras and lights; characters towards the camera is flags A bit 4 with bit 3.

Blending modes (0x63)

The values are the After Effects SDK’s PF_Xfer transfer modes. Normal is 2; cameras, lights and view cameras store 0. Dancing Dissolve has no value of its own: it is Dissolve (3) with transfer flag bit 1.

Value	Mode	Value	Mode
0	Normal (cameras and lights)	20	Silhouette Luma
2	Normal	21	Luminescent Premultiply
3	Dissolve	22	Alpha Add
4	Add	23	Classic Color Dodge
5	Multiply	24	Classic Color Burn
6	Screen	25	Exclusion
7	Overlay	26	Difference
8	Soft Light	27	Color Dodge
9	Hard Light	28	Color Burn
10	Darken	29	Linear Dodge
11	Lighten	30	Linear Burn
12	Classic Difference	31	Linear Light
13	Hue	32	Vivid Light
14	Saturation	33	Pin Light
15	Color	34	Hard Mix
16	Luminosity	35	Lighter Color
17	Stencil Alpha	36	Darker Color
18	Stencil Luma	37	Subtract
19	Silhouette Alpha	38	Divide

Value 1 has not been seen.

Layer types (0x83) and subtypes (0x8B)

Type	Layer	Subtype at 0x8B
0	AV layer: footage, solid, composition, null or adjustment layer	0
1	Light	0 Parallel, 1 Spot, 2 Point, 3 Ambient, 4 Environment (the SDK’s `AEGP_LightType` order)
2	Camera	0
3	Text	0
4	Shape	0
5	3D model	0
7	Parametric mesh	0 Cube, 1 Sphere, 2 Plane, 3 Torus, 4 Cone, 5 Cylinder

Type 6 has not been seen.

mdla and mdlv: 3D model layers

Layers of type 5 carry two more chunks after LIST:Gide. Neither is understood.

Chunk	Size	Contents
`mdla`	256	Unknown; all zero in the three samples that have it.
`mdlv`	8	A little-endian 64-bit value, 1 in the three samples.

Example

Reading a layer in a 24 frames a second composition (timebase 24576): a start time of 1200 ÷ 600 is 2 seconds; an in point of 24576 ÷ 24576 is 1 second of layer time; a stretch of 200 ÷ 100 is 200 %. The layer therefore appears in the composition at 2 + 1 × 200 ÷ 100 = 4 seconds. Flags bytes 04 00 07 at 0x25 to 0x27 mean Pixel Motion frame blending selected (but frame blending off), no flags B, and video, audio and effects on.

.AEP File Format – Layers