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Document AEP essential graphics
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@mbasaglia
mbasaglia committed May 1, 2023
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Expand Up @@ -154,6 +154,16 @@ Structure:

Each layer will show as a {sl:`LIST` `Layr`} in the {sl:`LIST` `Item`}.

The composition will also have other type of layer `LIST`s:

* {sl:`LIST` `DLay`}: Default view
* {sl:`LIST` `CLay`}: Custom views
* {sl:`LIST` `SLay`}: Side views
* {sl:`LIST` `SecL`}: Composition markers layer

If the comp uses {sl:essential graphics}, it will have the appropriate `LIST`s as well.


#### Assets

{sl:`idta`} type `7`. These can have different kinds of contents.
Expand Down Expand Up @@ -471,6 +481,128 @@ The effects in a later are listed under `ADBE Effect Parade`:
* {sl:`LIST` `tdgp`}: Parameter values, works like any other property list


### Essential Graphics

#### Definition

Essential graphics are defined in the following chunks inside the comp's {sl:`LIST` `Item`}:

* {sl:`LIST` `CIF0`}
* {sl:`LIST` `CIF2`}
* {sl:`LIST` `CIF3`}

They seem to have the same structure and (almost) identical values. But only `CIF3`
has data about groups:

* {sl:`LIST` `CIF3`}
* {sl:`LIST` `CpS2`}
* `CsCt`: seems to always have the value `0x1000000`.
* {sl:`Utf8`}: Name (Defaults to `Untitled`)
* {sl:`Utf8`}: Locale? (`en_US`)
* {sl:`CapS`}
* `CsCt`: seems to always have the value `0x1000000`.
* `CapL`: seems to always have the value `0`.
* {sl:`Utf8`}: Name (again, same value as before)
* {sl:`LIST` `CCtl`}: Item (repeated)

Items have the following common structure

* {sl:`LIST` `CCtl`}
* {sl:`LIST` `CpS2`}
* {sl:`Utf8`}: Name
* {sl:`LIST` `CapS`}
* {sl:`Utf8`}: Name (again)
* {sl:`Utf8`}: UUID
* {sl:`CTyp`}: item type
* {sl:`CprC`}: Flags
* Type-specific data

##### Comment

* {sl:`CTyp`}: `8`
* {sl:`Utf8`}: Comment string
* {sl:`Utf8`}: Comment string (again)
* {sl:`CprC`}: `0`

##### Group


* {sl:`CTyp`}: `8`
* {sl:`LIST` `StVc`}: Items
* {sl:`StVS`}: Count
* {sl:`Utf8`}: UUID of child items (repeated)
* {sl:`CprC`}: `0`

##### Property

* {sl:`CVal`}: Value
* {sl:`CDef`}: Default Value
* {sl:`Smin`}: Slider min value (only for scalar properties)
* {sl:`Smax`}: Slider max value (only for scalar properties)
* {sl:`CDim`}: Number of dimenstions (only for vector properties)
* {sl:`CprC`}: `1`
* {sl:`LIST` `CPrp`}
* {sl:`CCId`}: Composition ID (same as the one in {sl:`idta`}).
* {sl:`CLId`}: Layer ID (same as the one in {sl:`ldta`}).
* {sl:`Utf8`}: JSON-ecoded path.

The JSON is a dict where the key is a string containing a number and the values are dicts like this:

* `index`: Index for like shape groups and such, or the value `4294967295` (`0xffffffff`) is used when there is no index
* `matchName`: Match name as per usual

To find the property, something like this might work:

```python
CCId = 15
CLId = 18
json_data = {
"0": {
"index":4294967295,
"matchName":"ADBE Root Vectors Group"
},
"1": {
"index":0,
"matchName":"ADBE Vector Group"
},
"2": {
"index":4294967295,
"matchName":"ADBE Vectors Group"
},
"3": {
"index":2,
"matchName":"ADBE Vector Graphic - Fill"
},
"4": {
"index":4294967295,
"matchName":"ADBE Vector Fill Opacity"
}
}

property = get_layer(CCId, CLId)

for item in json_data.values():
if item["index"] == 0xffffffff:
property = property.property(item["matchName"])
else:
property = property.properties[item["index"]]
```


The values in `Smin`, `Smax`, `CVal`, `CDef` depends on the type, refer to {sl:`CTyp`} for their representation.


#### Overrides

Defined in the precomp layer under match name `ADBE Layer Overrides`

* {sl:`tdmn`}: `ADBE Layer Overrides`
* {sl:`LIST` `OvG2`}
* {sl:`LIST` `CPrp`}: (repeated)
* {sl:`Utf8`}: UUID of the essential property
* {sl:`LIST` `tdgp`}: Property groups with the matching properties defined as usual.


## Match Names

Follows a list of known match names grouped by object type.
Expand All @@ -496,7 +628,7 @@ ADBE Marker : Markers
ADBE Mask Parade : prop=masksProperties
ADBE Plane Options Group :
ADBE Data Group :
ADBE Layer Overrides :
ADBE Layer Overrides : Essential graphincs values
ADBE Source Options Group :

{aep_mn}
Expand Down Expand Up @@ -1676,6 +1808,71 @@ Mask Modes:
* 6: Difference


### `CCId`

Composition ID for essential graphics properties (`uint32`)

### `CLId`

Layer ID for essential graphics properties (`uint32`)

### `Smin`

Essential graphics slider minimum value.

Representation depends on the value of the previous {sl:`CTyp`}.

### `Smax`

Essential graphics slider maximum value.

Representation depends on the value of the previous {sl:`CTyp`}.

### `CVal`

Essential graphics property current value.

Representation depends on the value of the previous {sl:`CTyp`}.

### `CDef`

Essential graphics property default value.

Representation depends on the value of the previous {sl:`CTyp`}.


### `CTyp`

`uint32` with the essential graphics item type


| Name |Type | Value Format |
|-----------|-----|-----------------|
| Scalar | `2` | `float64` |
| Color | `4` | `float32[4]` |
| Position | `5` | `float64[2]` |
| Comment | `8` | |
| Vector | `9` | `float64[4]` |
| Group |`10` | |


### `CprC`

Essential graphics flags (4bytes)

* Is property (3, 0)

### `StVS`

Essential graphics group item count


|Name |Size| Type |
|-----------|----|----------|
| Count | 1 | `uint8` |
| | 3 | |


### `LIST` `Fold`

Top level item.
Expand Down Expand Up @@ -1812,10 +2009,6 @@ Contains a {sl:`LIST` `tdbs`} and a {sl:`LIST` `otky`} to define a shape proper

Contains a sequence of {sl:`otda`} with the orientation data for each keyframe.

### `LIST` `CpS2`

They contain a {sl:`CsCt`} and two {sl:`Utf8`}, the last of which seems to
contain a locale name (eg: `en_US`)

### `LIST` `Als2`

Expand Down Expand Up @@ -1929,8 +2122,46 @@ Contains:
* {sl:`opti`} with asset data


Gradient XML
------------
### `LIST` `CIF0`

See {sl:`LIST` `CIF3`}.

### `LIST` `CIF2`

See {sl:`LIST` `CIF3`}.

### `LIST` `CIF3`

{sl:Essential Graphics} Definition.

### `LIST` `CCtl`

Essential graphics item.


### `LIST` `CpS2`

Essential graphics header.


### `LIST` `StVc`

Essential graphics group items

### `LIST` `CPrp`

Essential graphics property definition

### `LIST` `OvG2`

Essential graphics override property identifiers

### `LIST` `CPrp`

Essential graphics override property identifier


## Gradient XML

Gradient data seems to be stored in a convoluted XML structure.

Expand Down Expand Up @@ -2058,8 +2289,7 @@ You should treat the midpoint value for opacity stops in a similar way as to the

Once you have both the color and opacity values, the final lottie array is simply a concatenation of the two.

XMP Metadata
------------
## XMP Metadata

After the RIFX data, an AEP file also contains some XML in the
[XMP](https://en.wikipedia.org/wiki/Extensible_Metadata_Platform) format.
Expand All @@ -2068,8 +2298,7 @@ This section contains the version of AfterEffects, when the file has been
created and modified, and related info.


XML Project Format
------------------
## XML Project Format

Aftereffects allows you to save the project as XML.

Expand Down Expand Up @@ -2109,8 +2338,7 @@ Elements with the {sl:`bdata`} attribute have their binary data hex encoded in s
You can parse their data the same way as you'd do in RIFX.


Resources
---------
## Resources

* [aftereffects-aep-parser](https://github.com/boltframe/aftereffects-aep-parser) A basic AEP parser written in Go.
* [Multimedia Programming Interface and Data Specifications 1.0](https://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/Docs/riffmci.pdf) RIFF specs PDF.
Expand Down

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