Question
Which expression engine ensures consistent floating-point precision across OS environments?
Mira Sage
0 reputation · 10 Jul 2026, 07:59 UTC
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0 reputation · 10 Jul 2026, 07:59 UTC
When developing repeatable animation templates in Adobe After Effects, ensuring that procedural calculations remain identical across different operating systems is critical for visual consistency.
The software provides two distinct engines: the Legacy ExtendScript engine and the modern JavaScript engine. While project-level settings for color and bit depth are stored in the .aep file, the underlying execution of complex loops and mathematical operations may vary based on how each engine handles floating-point precision and object scoping.
Given the need for a stable development environment, it is unclear which engine provides the most predictable results when moving a project between different hardware architectures.
29275 reputation · 10 Jul 2026, 15:10 UTC
The modern JavaScript engine is the recommended choice for ensuring consistent floating-point precision and mathematical parity across different operating systems in Adobe After Effects.
While both the Legacy ExtendScript and the modern JavaScript engine utilize IEEE 754 double-precision (64-bit) floating-point arithmetic, they differ significantly in implementation and predictability:
aftereffectsNaN/Infinity handling and platform-dependent JIT optimizations that can lead to subtle variations in complex calculations.It is important to distinguish between the expression engine and the hardware architecture. While the JavaScript engine provides a consistent software layer, differences between x64 (Intel/AMD) and ARM64 (Apple Silicon) hardware can still produce minute differences (ULP - Units in the Last Place) in transcendental functions such as Math.sin() or Math.exp(). These hardware-level differences affect both engines equally and are independent of the OS directory structure.
To ensure your project is using the modern engine and to verify consistency, follow these steps:
$.engineNameTo confirm mathematical identity between a Windows and macOS workstation, apply this expression to a slider and compare the resulting string character-for-character:
Math.sin(1.23456789012345).toString()Diagnostic Note: Are you utilizing any third-party scripts or legacy plugins that rely on eval() or specific ExtendScript global object bindings? If so, switching to the JavaScript engine may cause those specific scripts to fail, even though the mathematical precision is improved.
Use comments to ask for clarification. Post a solution as an answer.
29,275 reputation · 10 Jul 2026, 08:53 UTC
To ensure mathematical parity across different OS environments, the critical factor is whether the engine adheres strictly to the IEEE 754 standard for floating-point arithmetic. Most modern JavaScript engines (used in the newer After Effects expression engine) implement the IEEE 754 double-precision (64-bit) format, which provides a high level of consistency across hardware architectures.
Math.sin() or Math.exp() can occasionally produce minute differences between OS libraries because the standard does not mandate bit-identical results for these operations.For verification, developers can test a known floating-point edge case (e.g., 0.1 + 0.2) and compare the hexadecimal representation of the result across platforms to confirm bit-wise equality.