[After Effects] Help needed compiling Cryptomatte_AE for ExtendScript manifest access

[marynagoretti]

Hi there,

I am trying to customize the Cryptomatte plugin for After Effects to make the manifest parameter readable via ExtendScript for an automation project.

I have attempted to build the plugin from source (fnordware/ProEXR) using Visual Studio. The build completes successfully, but After Effects fails to recognize the resulting .aex file (it doesn't show up in the effects list).

I suspect I might be missing some specific environment configurations or resource linking steps. Could anyone (perhaps @fnordware) provide some guidance on:

1. Build Settings: Are there specific Visual Studio or Adobe SDK versions required for a compatible build?
2. Resource Files: How should I ensure the PiPL and other resources are correctly linked so AE can load the plugin?
3. ExtendScript: Any tips on how to expose the manifest string so it can be accessed as a property via script?

Any help would be greatly appreciated!

Environment details
OS: Windows 10
After Effects Version: 25.2 (2025)
AE SDK Version: 25.2
Compiler: Visual Studio 2022

[fnordware]

@marynagoretti, FYI, the latest Cryptomatte plug-in code is part of this repo on GitLab.

The Cryptomatte plug-in actually ships with AE. When I work on it, I disable the installed version and build a new version in AE's plug-ins folder, which is not what Visual Studio defaults to. So unless you're changing the Visual Studio output or copying the built plug-in, I wouldn't expect it to show up.

Are you sure it's possible to make the parameter available to ExtendScript? After Effects doesn't have a string parameter type, so I had to make an "Arbitrary Data" parameter, which is generally not available to scripting. The OpenEXR file importer includes "ProEXR Comp Creator" (aka import as composition) functionality to automatically set up Cryptomatte and related plug-ins; it can do this because it's using C++ AEGP calls, not ExtendScript. If you have a specific workflow you want to implement, you could make your own AEGP plug-in based on the Comp Creator.

[marynagoretti]

Hi Brendan,
Thank you so much for your detailed explanation!

Regarding the build issue: I did change the output path to a subfolder within the AE Plug-ins directory (/myBuilds) and temporarily disabled the original plugin, but for some reason, AE still wouldn't load it. I'll double-check my PiPL settings.

To clarify my goal: I’m trying to allow the loading of an external manifest. The EXR files I’m working with don’t have human-readable layer names, so I wanted to provide a manifest file separately to make the Cryptomatte selections clear and manageable. My plan was to build a custom UI in ExtendScript that parses this manifest to organize and automate the selection process.
I wasn't sure if the manifest parameter was accessible via ExtendScript, and your explanation about "Arbitrary Data" clarifies why I was struggling.

If I understand your suggestion correctly, I would need to:

1. Use the ProEXR source code as a base.
2. Create a new AEGP plugin that identifies the Cryptomatte effect on a layer.
3. Extract the manifest data using C++ and then "pass" that data to ExtendScript.
   To be honest, this sounds much more complex than I anticipated, as my C++ and SDK knowledge is quite limited. I was hoping for a more straightforward way to automate selections via ExtendScript.

Given that I'm not a specialist in low-level plugin development, what would you recommend as the most "script-friendly" path to achieve this? Is there perhaps a simpler way to "force" a manifest string into the effect, or should I look into a different approach entirely?
Thank you again for your time and guidance!

Best regards,
Maryna

[fnordware]

Have you tried importing your EXR as a composition or running Create ProEXR Layer Comps? If the EXR file has the manifest embedded, this will put it into Cryptomatte for you. If the file has a sidecar manifest and the EXR file indicates as much (like the sample here does), then it should also load it. If all else fails you can copy and paste the manifest in.

[marynagoretti]

Thank you so much for the tip!

You were absolutely right—I had previously only tried importing the EXR as Footage, which was causing the manifest to be unreadable. By using the Import as Composition method instead, the manifest is parsed perfectly and all the names are now human-readable. This is a huge step forward!

Now that the manifest is correctly loaded, my next goal is to automate the selection process within the Cryptomatte effect using ExtendScript. My objective is to automatically generate multiple mask layers based on specific Cryptomatte selections.

In your experience, is the "Selection" parameter (the field where the matte IDs are stored) easily accessible and writable via ExtendScript? Or are there any "Arbitrary Data" limitations even for the selection string?

Thank you again for pointing me in the right direction!

[marynagoretti]

Hi Brendan,
I’m sorry to bother you again so soon!
I previously asked about Arbitrary Data because I was trying to understand why I couldn’t "see" the Selection field via script. I don't want to take up too much of your time, but I’ve done some deeper technical testing and I’ve hit a specific wall that I think only you can clarify.

My workflow involves a template where I replace EXR files. The problem is that object names in the manifest change between renders, so I can't use static Animation Presets (.ffx).

Since the "Selection" property is not exposed to the AE Property stream (it doesn't show up in a numProperties scan), I have no way to programmatically tell Cryptomatte which ID to pick based on a dynamic manifest search.

Would it be possible to expose the Selection string as a standard, scriptable AE property?
If I could use something like effect("Cryptomatte").property("Selection").setValue(newNameFromJSON), I could fully automate the update of my templates regardless of name changes. Currently, it seems to be a "black box" that requires manual typing/pasting for every single layer.

Thank you again for your incredible patience and for everything you've done for After Effects users!

[fnordware]

Maryna, I'm afraid I don't know of a way to expose the selection parameter text to scripting. As far as After Effects is concerned, that parameter (which includes the layer name, selection string, and manifest) is opaque binary data. The only way to set it up in an automatic fashion would be with a C++ AEGP plug-in that knows how to manipulate the data.

While the names of objects in your 3D scenes are liable to change, there are other ways to tag things in Cryptomatte, if your 3D program allows. If you could tag objects by their use in the comp, then a template would be able to take in new shots without having to edit the Cryptomatte selection string.

[marynagoretti]

Hi Brendan,
Thank you so much for your previous spent time and for the insights!
I wanted to update you and let you know that I eventually found a "backdoor" to achieve this without a C++ AEGP plugin. Since After Effects can save projects in XML format (.aepx), I noticed that the "opaque binary data" you mentioned is actually stored as a hex string.
By parsing the .aepx as a text file, I was able to:

1. Extract the JSON manifest directly from the EXR binary data
2. Reconstruct the hex string for the Cryptomatte selection
3. Inject the new hex string back into the XML and reload the project.
   It works perfectly and allows for a completely automated sync between the EXR manifest and the Cryptomatte effect parameters!
   Thanks again for your kindness and for creating such indispensable tools for our industry.

[fnordware]

Whoa, nice one! Bravo, Maryna.