Is there a way to use interpolation on an extended video?

[Lainier]

I'm experimenting with the video extend feature using WAN 2.1 i2v model and I'm getting good results extending 5 seconds videos to 10 seconds. In i2v settings I set video frames to 81 and I use a single <extend:81> in the prompt. But extended videos are a mess if i turn on interpolation in i2v settings. The first video generated by i2v is interpolated from 16 fps to 32 fps and looks good, but the extended video runs for 15 seconds instead of 10 and in slow motion. I suppose this happens because the extend video feature is extending a video which is running at 32 fps, while the extended video is supposed to run at 16 fps. I need no know if there is a way to properly use interpolation on the final extended video, not in the first generated video.

I could also use another software to interpolate the extended video, but I don't want to lose quality by reencoding ;)