Influence on render speed only by changing the render comp dimension

Question

I have a question perhaps a little strange. I built an entire project in 4K, all my comps, pre-comps and layers were created in the dimensions 3840 x 2160. But when the project was ready I had to reduce it to 2k resolution of 2560 x 1440. So I just changed the resolution from render composition to 2k and parented all my pre-comps and layers placed in the render comp to a null object and scaled that null object by 66.7% to fit 2k resolution. Except the dimension of my render comp all the other pre-comps and layers continued with the 4k dimension, just scaled down to fit the 2k dimension of the render comp. My question is, with just the render comp in 2k dimension and the rest of the pre-comps and layers in 4K would have the same rendering time as an entire project of comps, pre-comps and layers built natively in 2k? As if only changing the resolution of the render comp would influence a lot on the rendering speed of the project.

Mylenium · Answer

Long and short: No. AE is a full buffer renderer, meaning it has to calculate the entire frame at full resolution for every step before handing over the buffer to the next effect or applying transform functions to it. Except for a few things that come with continuous rasterization/ collapsed transformations it has no way of concatenating and optimizing render calls such as node-based compositing apps can do and obviously AE also does not use tile-based rendering, scanlines or any other such methods that would allow it to "skip" pixels it would not need to calculate at lower resolutions. Therefore just changing the main render comp or for that matter only some of the sub-comps will have almost no impact on render performance. This is a case of "all or nothing" where you would have to consequently change all compositions and assets to truly see some serious speed gains.

Mylenium

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