.AEP File Format – Properties and keyframes

LIST:tdgp: property group

The layer’s root group and every named group below it: Transform, Masks, Effects, one mask, one effect’s parameters, a shape group, a layer style.

A child’s body is every chunk between its tdmn and the next one:

The group’s tdsn holds the six characters -_0_/- when the group has no name of its own (After Effects then shows the match name’s localised default), the visible name for groups that carry one (Mask 1, Group 1, Fill 1, a renamed effect), and an empty string on a layer’s root group.

Order and omitted children

After Effects reads a group’s children by match name in a fixed order, scanning forwards; a child that appears too early is skipped as if absent. The order AE 2025 and 2026 write:

• Root group: ADBE Marker; then ADBE Time Remapping (AV layers), ADBE Text Properties (text) or ADBE Root Vectors Group (shape); ADBE Mask Parade, ADBE Effect Parade, ADBE Transform Group, ADBE Light Options Group or ADBE Camera Options Group, ADBE Layer Styles, ADBE Plane Options Group, ADBE Extrsn Options Group, ADBE Material Options Group, ADBE Audio Group, ADBE Data Group, ADBE Layer Overrides, ADBE Layer Sets, ADBE Source Options Group, ADBE Group End. AE 15 has no Layer Sets or Source Options Group.
• Transform group: ADBE Anchor Point, ADBE Position, ADBE Position_0, _1, _2, ADBE Scale, ADBE Orientation, ADBE Rotate X, Y, Z, ADBE Opacity, ADBE Envir Appear in Reflect, ADBE Group End.

Not every property is written. Empty Masks, Effects, Motion Trackers and Text Animators groups are left out, and so are many streams that hold their default: most AV layers in the samples have no Anchor Point, Position or Scale stream at all. A reader supplies the default for a missing property.

tdmn: match name (40 bytes)

The match name of the child that follows, ASCII, padded with zeros to 40 bytes (ADBE Position, ADBE Effect Parade). Effect parameters are named after the effect with a four-digit index, as in ADBE Gaussian Blur 2-0001; -0000 is a hidden first parameter that every effect carries. tdmn also appears in LIST:parT and LIST:EfDf.

tdsb: group and stream flags (4 bytes)

All other bits are 0 in about 1.1 million samples. A visible stream stores 0x1 and a hidden one 0x3. An unseparated Position stores 0x1 on ADBE Position and 0x3 on _0, _1 and _2; once separated, 0x803 on the leader and 0x1 on the three followers, which then hold the values and keyframes.

LIST:tdbs: property stream

The order is always tdsb tdsn tdb4 (cdat | LIST:list) [Utf8] [tdum tduM | tdpi tdps | tdli].

Stream kinds

The value layout depends on tdb4: its dimension count, bit 1 of its stream flags (the single-ease layout) and its valueless flag.

Sizes are in bytes. Valueless streams keep their real value in the container named in the last column; their cdat and the value part of their keyframes are placeholders.

Expressions

An expression is a Utf8 right after the value. tdb4 records it twice: 0x78 holds 0x01000000 exactly when the expression is present, and bit 0 of 0x77 is set when it is disabled.

Static and animated

When the first keyframe is added, After Effects replaces the cdat with a keyframe list and changes only these bytes of tdb4: it clears bit 0 of the stream flags, sets 0x44 to 1, clears bit 0 of 0x4F, and zeroes the stored keyframe record at 0x48 to 0x73. Removing the last keyframe does the reverse, and the record keeps the removed key’s interpolation and spatial flags. A stream that was never set also has zeros for the time base and category, which become real values once it is animated.

tdb4: stream metadata (124 bytes)

Stream flags (0x04)

Type flags (0x3B) and category (0x3C)

Bit 0 of 0x3B marks a colour and bit 4 appears only on Orientation. Bits 2 and 3 and the category values are not decoded beyond this table.

cdat: static value

• Without stream-flag bit 1 (numbers, menus): dimensions × 5 doubles. The first dims are the value; the rest, in the places of the eases, are 0. 40, 80 or 120 bytes.
• With stream-flag bit 1 (spatial, colour): dimensions × 3 doubles: the value, then in and out tangents, which are 0. 48 or 72 bytes for points, 96 for a colour.
• Orientation: three little-endian doubles, the X, Y and Z angles in degrees (24 bytes).
• Other valueless streams: 4 zero bytes.

tdum, tduM, tdli, tdpi and tdps

The bounds pair appears on numeric layer streams that are not angles, menus, checkboxes, colours or spatial streams, for example Opacity 0.0 / 100.0 (in the user’s units, though the value itself is stored as a fraction), Index of Refraction 1.0 / 2.0, Plane Subdivision 2.0 / 256.0, and 0.0 / 0.0 as a placeholder on Scale, separated Position and Time Remapping. Effect parameters keep their real bounds in pard.

LIST:list and lhd3: typed lists

A header and, unless the list is empty, the items. Under a stream it is the keyframe list; it also holds guides, mask and shape vertices and render queue records.

The block size is 4 for keyframes and vertices, 2 for guides and 1 for render queue records. An empty guide list stores count 0 with 1, 1, 2 in the counters, and has no ldat. After Effects checks the counters against the count and refuses a file where they disagree.

ldat: keyframe items

Keyframes are sorted by time. Every item starts with the same 8 bytes:

Numbers, text and markers (stream-flag bit 1 clear)

From 0x08: the value, then the in speed, in influence, out speed and out influence, each as dims doubles. A 1-D item is 48 bytes, 2-D 88 and 3-D 128. Influences are fractions (0.33 is 33 %); After Effects’ default influence is the decimal 0.16666666667. Text and marker items are 16 bytes: 8 bytes at 0x08 that carry nothing, and interpolation 3 / 3 (hold).

Spatial, colour, Orientation, paths and gradients (bit 1 set)

• Spatial: dims doubles of value, then in tangent and out tangent as offsets from the value. 104 bytes for 2-D, 128 for 3-D.
• Colour: A, R, G, B (0–255), then 8 doubles that are 0. 152 bytes.
• Orientation: X, Y and Z angles as three little-endian doubles. 80 bytes.
• Paths and gradients: 8 bytes that carry nothing; the value is in LIST:omks or LIST:GCky. 64 bytes.

Interpreting keyframes

• Time. A key’s composition time is start time + (time ÷ time base) × stretch ÷ 100. Times need not fall on frames.
• Segment type. The segment from key A to key B uses A’s out type and B’s in type. Hold on A’s out side keeps A’s value until B.
• Temporal Bezier. For each dimension, with dt = tB − tA, A’s out speed so and influence io, and B’s in speed si and influence ii, the curve’s control points are (tA, vA), (tA + dt·io, vA + dt·io·so), (tB − dt·ii, vB − dt·ii·si) and (tB, vB).
• Spatial streams. The path from A to B is the cubic through vA, vA + A’s out tangent, vB + B’s in tangent and vB. The ease maps time to distance along it, with the same handle rule in (seconds, distance) from (0, 0) to (dt, arc length). The length is measured with each dimension scaled by the tdb4 multipliers.
• Auto-Bezier. With key flag bit 4, the stored ease is ignored: each side uses the slope between the neighbouring keys with influence 0.16666666667. With spatial flag bit 1, the tangents are out = (next − previous) ÷ 6 and in = −out.
• Continuous. With key flag bit 3 the out speed equals the in speed.
• Roving. A roving key’s stored time is derived from its share of the arc length between the surrounding fixed keys.
• Switching a key between Linear, Hold and Bezier does not rewrite its stored speeds and influences.

Orientation: LIST:otst, LIST:otky and otda

ADBE Orientation’s body is LIST:otst: first its LIST:tdbs stream (one dimension, valueless, type flags 0x18), then LIST:otky with one otda per keyframe, or one when static. otda is 24 bytes: the X, Y and Z angles in degrees as big-endian doubles. The stream’s cdat or keyframe values hold the same angles little-endian. A camera’s untouched Orientation can also be a bare 3-dimension LIST:tdbs without LIST:otst.

Example

A static Opacity of 50 % on an unstretched layer at 24 frames a second has a tdb4 with dimensions 1, stream flags 0x0001, time base 24576 (bytes 00 00 60 00 at 0x0C), type flags 0x08 and category 9; its cdat is 40 bytes beginning 3F E0 00 00 00 00 00 00 (0.5) followed by four zero doubles; then tdum 0.0 and tduM 100.0. A keyframe at 1 second on the same stream has time 24576 (00 00 60 00).