I had worked out how to do it using Projector and keyframes, but taking your suggestions and modifying them for my use is easier

I am only likely to want to rescale the occasional clip in a sequence, although sometimes it could be several, which would make the timeline unwieldy with a staircase of of individually attached effects, so I tried attaching Size and Position and Scale to the timeline when necessary, enabling keyframes and keyframing each adjustment as required. To achieve the desired effect I use Crop and Position first then Rescale.That gives me exactly what I was looking for. Thanks again.

The answer to the resolution problem came to me overnight when I remembered I had forgotten to attach the Auto Scale effect, I haven't done it for so long!

As to cropping and resizing, the manual says cropping can be keyframed but not how to achieve it. I found a work around by putting clips for resizing on a separate track, fine if only cropping one clip, but add a second clip and the first crop affects it as well, any change to the second clip crop affects the first one too.

I have found a way to achieve what I want using Projector with keyframes rather than Crop. Is that what the manual refers to when it says cropping is keyframable?

Do you want to Crop a clip (or more clips) to focus on a detail of the image? When to Crop to 50% and resize to Project Format you may lose a bit of resolution to the image.

Thanks for the tip, but I know that. I find I am no longer able to carry my HC-X1500 along with travel tripod and other gear in a backpack for any length of time, so I have been experimenting with using a GoPro instead. My Hero 12 shooting 10-bit log in 5.3k, with the addition of GoPro Labs firmware, can give outstanding results with the right settings. To allow a slight lossless zoom, reframing or better so-called macro (with an added lens) when needed, I want to shoot 5k and reduce it to 4k in post. 5.3k has approximately 1.9x the pixels of 4k, so a nearly 50% zoom should do it.

What is your Format Project? 2160p -> 3840 x 2160 pixels?

Do you want to resize the 5.3k clips (5312 x 2988) to 2160p, before inserting them in the Timeline?

Do you want to Crop a clip (or more clips) to focus on a detail of the image? When to Crop to 50% and resize to Project Format you may lose a bit of resolution to the image.

@IgorBeg probably has the best answer for this.

1. I want to export corrected clips as 2160p video.

2. I want to crop the occasional clip in a sequence to about 50% and resize it to match the others, in other words, zoom in.

I thought I knew how, but it has defeated me so far!