Possible quality degradation of Size filter?

Sorry to bother you, but thank you in advance for your time. This is what I want to do: Shoot footage in 4K, then crop it down to 1080p in Shotcut. This way I can tighten up the composition to make it look better. I know I can use the [Source: Crop] filter, but it doesn’t support Keyframes, Alternative is, I can use the [Size, Position & Rotate] filter, which does support keyframes, but I’m not sure if it’ll incur loss in quality. Here is why:

Let’s say I have a 3840x2160 clip, I only want the center 1920x1080 part of it. For the [Crop] filter, I believe it only cuts out the rest of it, so there is no quality loss. But for [Size] filter, how does it do it? Would it first resample the whole frame down to 1920x1080, then blow up the center 960x540 part to make it become 1920x1080? If so, the blowing up inevitably introduces some quality degradation.

So my question is: Is this how [Size] filter works? Or is it smart enough to know that no resampling is needed, just crop it???

Thank you for your help!

It does not first scale to the video mode resolution. It resamples the source image to the size specified in the filter (with some exceptions such as when preview scaling is on). So, if you have a 3840x2160 clip in a 1920x1080 project, add the filter, and zoom it to 3840x2160, there is basically no scaling. However, it is still going to use interpolation for sub-pixel positioning.

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To OP: See this thread for more details. This is a common question.

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Thank you, this is exactly what I wanted to know. Thank you!

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